Magnetic tape having characterized magnetic layer surface, magnetic tape cartridge, and magnetic tape device

ABSTRACT

A magnetic tape in which a vertical switching field distribution SFD of the magnetic tape is 1.5 or less, and in an environment with a temperature of 32° C. and a relative humidity of 80%, a frictional force F 45 ° on the surface of the magnetic layer with respect to an LTO8 head measured at a head tilt angle of 45° is 4 gf to 15 gf, and a standard deviation of a frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at each of head tilt angles of 0°, 15°, 30°, and 45° is 10 gf or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C119 to Japanese PatentApplication No. 2021-158782 filed on Sep. 29, 2021. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tapecartridge, and a magnetic tape device.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage such as data back-up or archives (for example, seeJP2016-524774A and US2019/0164573A1).

SUMMARY OF THE INVENTION

Further improvement of electromagnetic conversion characteristics isalways required for magnetic recording media. Accordingly, a magnetictape capable of exhibiting excellent electromagnetic conversioncharacteristics is desirable.

Meanwhile, the recording of data on a magnetic tape is normallyperformed by causing the magnetic tape to run in a magnetic tape deviceand causing a magnetic head to follow a data band of the magnetic tapeto record data on the data band. Accordingly, a data track is formed onthe data band. In addition, in a case of reproducing the recorded data,the magnetic tape is caused to run in the magnetic tape device and themagnetic head is caused to follow the data band of the magnetic tape,thereby reading data recorded on the data band.

In order to increase an accuracy with which the magnetic head followsthe data band of the magnetic tape in the recording and/or thereproducing, a system that performs head tracking using a servo signal(hereinafter, referred to as a “servo system”) is practiced.

In addition, it is proposed that dimensional information of a magnetictape during running in a width direction (contraction, expansion, or thelike) is obtained using the servo signal and an angle for tilting anaxial direction of a module of a magnetic head with respect to the widthdirection of the magnetic tape (hereinafter, also referred to as a “headtilt angle”) is changed according to the obtained dimensionalinformation (see JP6590102B and US2019/0164573A1, for example,paragraphs 0059 to 0067 and paragraph 0084 of JP6590102B). During therecording or the reproducing, in a case where the magnetic head forrecording or reproducing data records or reproduces data while beingdeviated from a target track position due to width deformation of themagnetic tape, phenomenons such as overwriting on recorded data,reproducing failure, and the like may occur. The present inventorsconsider that changing the head tilt angle as described above is one ofa unit for suppressing the occurrence of such a phenomenon.

For example, assuming that the head tilt angle is changed as describedabove, it is desirable that running stability of the magnetic tape ishigh, in a case of recording and/or reproducing data at different headtilt angles. It is considered that the high running stability of themagnetic tape can lead to, for example, the further suppressing of theoccurrence of the phenomenon described above.

Meanwhile, in recent years, magnetic tapes may be used in temperatureand humidity managed data centers.

Meanwhile, in the data center, power saving is necessary for reducingthe cost. For realizing the power saving, it is desired that themanagement conditions of an use environment of the magnetic tape in thedata center can be relaxed compared to the current state, or themanaging may not be necessary.

However, it is also assumed that, in a case where the managementconditions of the use environment are relaxed or not managed, themagnetic tape is used, for example, in a high temperature and highhumidity environment. Accordingly, a magnetic tape having excellentrunning stability in a case of recording and/or reproducing data atdifferent head tilt angles in a high temperature and high humidityenvironment is desirable.

One aspect of the present invention is to provide a magnetic tapecapable of exhibiting excellent electromagnetic conversioncharacteristics and having excellent running stability in a case ofrecording and/or reproducing data at different head tilt angles in ahigh temperature and high humidity environment.

According to an aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; and a magnetic layer containinga ferromagnetic powder, in which a vertical switching field distributionSFD of the magnetic tape is 1.5 or less, in an environment with atemperature of 32° C. and a relative humidity of 80%, a frictional forceF45° on a surface of the magnetic layer with respect to a LinearTape-Open (LTO) 8 head measured at a head tilt angle of 45° is 4 gf to15 gf, and a standard deviation of a frictional force F on the surfaceof the magnetic layer with respect to the LTO8 head measured at each ofhead tilt angles of 0°, 15°, 30°, and 45° (hereinafter, also simplyreferred to as a “standard deviation of a frictional force F” or a“standard deviation of F”) is 10 gf or less.

Hereinafter, the vertical switching field distribution SFD of themagnetic tape is also referred to as “vertical SFD”.

In one embodiment, the standard deviation of F may be 2 gf to 10 gf.

In one embodiment, the vertical SFD may be 0.5 to 1.5.

In one embodiment, a standard deviation of a curvature of the magnetictape in a longitudinal direction (hereinafter, also simply referred toas a “standard deviation of curvature”) may be 5 mm/m or less.

In one embodiment, the magnetic layer may contain inorganic oxide-basedparticles.

In one embodiment, the inorganic oxide-based particles may be compositeparticles of an inorganic oxide and a polymer.

In one embodiment, the magnetic layer may include carbon black.

In one embodiment, the magnetic tape may further include a non-magneticlayer containing a non-magnetic powder between the non-magnetic supportand the magnetic layer.

In one embodiment, the magnetic tape may further include a back coatinglayer containing a non-magnetic powder on a surface side of thenon-magnetic support opposite to a surface side provided with themagnetic layer.

In one embodiment, the magnetic tape may have a tape thickness of 5.2 μmor less.

According to another aspect of the present invention, there is provideda magnetic tape cartridge including the magnetic tape described above.

One aspect of the invention relates to a magnetic tape device includingthe magnetic tape described above.

In one embodiment, the magnetic tape device may further comprise amagnetic head,

the magnetic head may include a module having an element array having aplurality of magnetic head elements between a pair of servo signalreading elements, and

the magnetic tape device may change an angle θ formed by an axis of theelement array with respect to a width direction of the magnetic tapeduring running of the magnetic tape in the magnetic tape device.

According to one aspect of the present invention, it is possible toprovide a magnetic tape capable of exhibiting excellent electromagneticconversion characteristics and having excellent running stability in acase of recording and/or reproducing data at different head tilt anglesin a high temperature and low humidity environment. In addition,according to one aspect of the invention, it is possible to provide amagnetic tape cartridge and a magnetic tape device including themagnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a module of a magnetichead.

FIG. 2 is an explanatory diagram of a relative positional relationshipbetween a module and a magnetic tape during running of the magnetic tapein a magnetic tape device.

FIG. 3 is an explanatory diagram of a change in angle θ during therunning of the magnetic tape.

FIG. 4 is an explanatory diagram of a curvature of a magnetic tape in alongitudinal direction.

FIG. 5 shows an example of disposition of data bands and servo bands.

FIG. 6 shows a servo pattern disposition example of a linear tape-open(LTO) Ultrium format tape.

FIG. 7 is an explanatory diagram of a method for measuring the angle θduring the running of the magnetic tape.

FIG. 8 is a schematic view showing an example of the magnetic tapedevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

An aspect of the invention relates to a magnetic tape including anon-magnetic support, and a magnetic layer containing a ferromagneticpowder. A vertical switching field distribution SFD (vertical SFD) ofthe magnetic tape is 1.5 or less. In addition, in an environment with atemperature of 32° C. and a relative humidity of 80%, regarding africtional force on a surface of the magnetic layer with respect to anLTO8 head of the magnetic tape, a frictional force F₄₅° on the surfaceof the magnetic layer with respect to the LTO8 head measured at a headtilt angle of 45° is 4 gf to 15 gf, and a standard deviation of africtional force F on the surface of the magnetic layer with respect tothe LTO8 head measured at each of head tilt angles of 0°, 15°, 30°, and45° is 10 gf or less. In the invention and the specification, the“surface of the magnetic layer” is identical to a surface of themagnetic tape on the magnetic layer side. In addition, in terms of unit,“gf” represents gram weight and 1 N (Newton) is approximately 102 gf.

Vertical SFD

In the present invention and the present specification, the verticalswitching field distribution SFD (vertical SFD) of the magnetic tape isa switching field distribution measured in a vertical direction of themagnetic tape. The “vertical direction” described regarding theswitching field distribution is a direction orthogonal to the surface ofthe magnetic layer, and can also be referred to as a thicknessdirection. In the present invention and the present specification, thevertical switching field distribution SFD of the magnetic tape is avalue obtained by the following method at a measurement temperature of25° C. using a vibrating sample magnetometer.

A sample piece for measurement is cut out from the magnetic tape to bemeasured. A size of the sample piece may be any size that can beintroduced into a vibrating sample magnetometer used for themeasurement. Regarding the sample piece, using the vibrating samplemagnetometer, a magnetic field is applied to a vertical direction of asample piece (direction orthogonal to the surface of the magnetic layer)with a maximum applied magnetic field of 3979 kA/m, a measurementtemperature of 25° C., and a magnetic field sweep speed of 8.3 kA/m/sec,and a magnetization strength of the sample piece with respect to themaximum applied magnetic field is measured. The measured value isobtained as a value obtained by subtracting magnetization of a sampleprobe of the vibrating sample magnetometer as background noise. In themagnetic field-magnetization curve (referred to as a “M-H curve”)obtained by such measurement, a magnitude H of a magnetic field in whicha magnetization strength M becomes zero is defined as a coercivity Hc(unit: Oe). In addition, among peaks seen in a differential curve in acase where the magnetization is differentiated by the magnetic field, ahalf width of the peak in the magnetic field higher than 2000 Oe isdefined as HPW (unit: Oe). The “HPW” is an abbreviation for the halfpeak width. The SFD is obtained by SFD=HPW Hc. In addition, regardingthe unit, 1 Oe (1 oersted)=79.6 A/m. The measurement temperature is atemperature of the sample piece. By setting the atmosphere temperaturearound the sample piece to the measurement temperature (25° C.), thetemperature of the sample piece can be set to the measurementtemperature (25° C.) by realizing temperature equilibrium.

The vertical SFD of the magnetic tape is 1.5 or less, preferably 1.3 orless, and more preferably 1.0 or less, from a viewpoint of improving theelectromagnetic conversion characteristics. The vertical SFD of themagnetic tape can be, for example, 0.1 or more, 3.0 or more, or 0.5 ormore, or can be less than the value exemplified here. It is preferablethat the value of the vertical SFD is small, from a viewpoint of furtherimproving the electromagnetic conversion characteristics. The verticalSFD of the magnetic tape can be, for example, controlled by a well-knownmethod such as adjusting homeotropic alignment process conditions.

Head Tilt Angle

Next, for describing the head tilt angle, first, the LTO8 head will bedescribed hereinafter. In addition, a reason why it is considered thatthe phenomenon occurring during the recording or during the reproducingdescribed above can be suppressed by tilting an axial direction of themodule of the magnetic head with respect to the width direction of themagnetic tape while the magnetic tape is running will also be describedlater.

In the invention and the specification, the “LTO8 head” is a magnetichead according to the LTO8 standard. For the measurement of thefrictional force, a magnetic head mounted on an LTO8 drive may beextracted and used, or a commercially available magnetic head may beused as the magnetic head for the LTO drive. Here, the LTO8 drive is adrive (magnetic tape device) according to the LTO8 standard. The LTO9drive is a drive according to the LTO9 standard, and the same applies todrives of other generations. In addition, in a case of measuring africtional force F on the surface of the magnetic layer with respect tothe LTO8 head at each of head tilt angles of 0°, 15°, 30°, and 45°, inthe measurement at each head tilt angle, new (that is, unused) LTO8 headis used for each measurement. In addition, the LTO8 is used as a headfor measuring the frictional force considering that the LTO8 standard isthe standard that can cope with high-density recording in recent years,and the magnetic tape is not limited to a magnetic tape used in the LTO8drive. The magnetic tape may perform the recording and/or reproducing ofdata in the LTO8 drive, may perform the recording and/or reproducing ofdata in the LTO9 drive or a next-generation drive, or may perform therecording and/or reproducing of data in a drive in earlier generationsof the LTO8 such as LTO7.

The LTO8 head includes three modules each having an element arrayincluding a plurality of magnetic head elements between a pair of servosignal reading elements. The three modules are arranged in the LTO8 headin arrangement of “recording module-reproducing module-recording module”(total number of modules: 3).

Each module includes an element array including 32 magnetic headelements in total between a pair of servo signal reading elements, thatis, arrangement of elements. The module including a recording element asthe magnetic head element is a recording module for recording data onthe magnetic tape. The module including a reproducing element as themagnetic head element is a reproducing module for reproducing datarecorded on the magnetic tape. In the LTO8 head, the three modules arearranged so that an axis of the element array of each module is orientedin parallel. The “parallel” does not mean only parallel in the strictsense, but also includes a range of errors normally allowed in thetechnical field of the invention. For example, the range of errors meansa range of less than ±10° from an exact parallel direction.

The head tilt angle in the frictional force measurement is a head tiltangle of the LTO8 head in the reproducing module.

In each element array, the pair of servo signal reading elements and theplurality of magnetic head elements (that is, recording elements orreproducing elements) are arranged to be in a straight line spaced apartfrom each other. Here, the expression that “arranged in a straight line”means that each magnetic head element is arranged on a straight lineconnecting a central portion of one servo signal reading element and acentral portion of the other servo signal reading element. The “axis ofthe element array” in the present invention and the presentspecification means the straight line connecting the central portion ofone servo signal reading element and the central portion of the otherservo signal reading element.

Next, the configuration of the module and the like will be furtherdescribed with reference to the drawings. However, the aspect shown inthe drawings is an example and the invention is not limited thereto.

FIG. 1 is a schematic view showing an example of a module of a magnetichead. The module shown in FIG. 1 includes a plurality of magnetic headelements between a pair of servo signal reading elements (servo signalreading elements 1 and 2). The magnetic head element is also referred toas a “channel”. “Ch” in the drawing is an abbreviation for a channel.The module shown in FIG. 1 includes a total of 32 magnetic head elementsof Ch0 to Ch31. The reproducing module of the LTO8 head includes a totalof 32 reproducing elements of Ch0 to Ch31.

In FIG. 1 , “L” is a distance between the pair of servo signal readingelements, that is, a distance between one servo signal reading elementand the other servo signal reading element. In the module shown in FIG.1 , the “L” is a distance between the servo signal reading element 1 andthe servo signal reading element 2. Specifically, the “L” is a distancebetween a central portion of the servo signal reading element 1 and acentral portion of the servo signal reading element 2. Such a distancecan be measured by, for example, an optical microscope or the like.

FIG. 2 is an explanatory diagram of a relative positional relationshipbetween the module and the magnetic tape during running of the magnetictape in the magnetic tape device. In FIG. 2 , a dotted line A indicatesa width direction of the magnetic tape. A dotted line B indicates anaxis of the element array. An angle θ can be the head tilt angle duringthe running of the magnetic tape, and is an angle formed by the dottedline A and the dotted line B. During the running of the magnetic tape,in a case where the angle θ is 0°, a distance in a width direction ofthe magnetic tape between one servo signal reading element and the otherservo signal reading element of the element array (hereinafter, alsoreferred to as an “effective distance between servo signal readingelements”) is “L”. On the other hand, in a case where the angle θexceeds 0°, the effective distance between the servo signal readingelements is “Lcosθ” and the Lcosθ is smaller than the L. That is,“Lcosθ<L”.

As described above, during the recording or the reproducing, in a casewhere the magnetic head for recording or reproducing data records orreproduces data while being deviated from a target track position due towidth deformation of the magnetic tape, phenomenons such as overwritingon recorded data, reproducing failure, and the like may occur. Forexample, in a case where a width of the magnetic tape contracts orextends, a phenomenon may occur in which the magnetic head element thatshould record or reproduce at a target track position records orreproduces at a different track position. In addition, in a case wherethe width of the magnetic tape extends, the effective distance betweenthe servo signal reading elements may be shortened than a spacing of twoadjacent servo bands with a data band interposed therebetween (alsoreferred to as a “servo band spacing” or “spacing of servo bands”,specifically, a distance between the two servo bands in the widthdirection of the magnetic tape), and a phenomenon in that the data isnot recorded or reproduced at a part close to an edge of the magnetictape can occur.

With respect to this, in a case where the element array is tilted at theangle θ exceeding 0°, the effective distance between the servo signalreading elements becomes “Lcos θ” as described above. The larger thevalue of θ, the smaller the value of Lcos θ, and the smaller the valueof θ, the larger the value of Lcos θ. Accordingly, in a case where thevalue of θ is changed according to a degree of dimension change (thatis, contraction or expansion) in the width direction of the magnetictape, the effective distance between the servo signal reading elementscan be brought closer to or matched with the spacing of the servo bands.Therefore, during the recording or the reproducing, it is possible toprevent the occurrence of phenomenons such as overwriting on recordeddata, reproducing failure, and the like caused in a case where themagnetic head for recording or reproducing data records or reproducesdata while being deviated from a target track position due to widthdeformation of the magnetic tape, or it is possible to reduce afrequency of occurrence thereof.

FIG. 3 is an explanatory diagram of a change in angle θ during therunning of the magnetic tape.

The angle θ at the start of running, θ_(initial), can be set to, forexample, 0° or more or more than 0°.

In FIG. 3 , a central diagram shows a state of the module at the startof running

In FIG. 3 , a right diagram shows a state of the module in a case wherethe angle θ is set to an angle θ_(c) which is a larger angle than theθ_(initial). The effective distance between the servo signal readingelements Lcosθ_(e) is a value smaller than Lcosθ_(initial) at the startof running of the magnetic tape. In a case where the width of themagnetic tape is contracted during the running of the magnetic tape, itis preferable to perform such angle adjustment.

On the other hand, in FIG. 3 , a left diagram shows a state of themodule in a case where the angle θ is set to an angle θ_(e) which is asmaller angle than the θ_(initial). The effective distance between theservo signal reading elements Lcosθ_(e) is a value larger thanLcosθ_(initial) at the start of running of the magnetic tape. In a casewhere the width of the magnetic tape is expanded during the running ofthe magnetic tape, it is preferable to perform such angle adjustment.

As described above, the change of the head tilt angle during the runningof the magnetic tape can contribute to prevention of the occurrence ofphenomenons such as overwriting on recorded data, reproducing failure,and the like caused in a case where the magnetic head for recording orreproducing data records or reproduces data while being deviated from atarget track position due to width deformation of the magnetic tape, orto reduction of a frequency of occurrence thereof.

Meanwhile, the recording of data on the magnetic tape and thereproducing of the recorded data are performed by bringing the surfaceof the magnetic layer of the magnetic tape into contact with themagnetic head and sliding. The inventors considered that, during suchsliding, in a case where the head tilt angle changes, a contact statebetween the magnetic head and the surface of the magnetic layer canchange and this can be a reason of a decrease in running stability.Specifically, the inventors surmised that, in a case where the contactstate between the surface of the magnetic layer of the magnetic tape andthe magnetic head (for example, a contact state between a portion nearan edge of the module of the magnetic head and the surface of themagnetic layer) changes greatly depending on the difference in the headtilt angle, the running stability decreases and such decrease in runningstability can become more remarkable in a high temperature and highhumidity environment.

Based on the surmise described above, the present inventors conductedintensive studies. As a result, it is newly found that, regarding thefriction property of the magnetic tape, in the environment with thetemperature of 32° C. and the relative humidity of 80%, by setting thefrictional force F45° on the surface of the magnetic layer with respectto the LTO8 head measured at the head tilt angle 45°, and the standarddeviation of the frictional force F on the surface of the magnetic layerwith respect to the LTO8 head measured at each of the head tilt anglesof 0°, 15°, 30°, and 45° to be in the ranges described above,respectively, it is possible to improve running stability in a case ofperforming the recording and/or reproducing of data at different headtilt angles in the high temperature and high humidity environment. Thetemperature and humidity of the measurement environment are used asexemplary values of the temperature and humidity of the high temperatureand high humidity environment. Accordingly, the environment in which thedata is recorded on the magnetic tape and the recorded data isreproduced is not limited to the environment with the temperature andthe humidity described above. The head tilt angle in a case of measuringthe frictional force is also used as an exemplary value of the anglethat can be used in a case of performing the recording and/orreproducing of data by changing the head tilt angle during the runningof the magnetic tape. Accordingly, the head tilt angle in a case wherethe data is recorded on the magnetic tape and the recorded data isreproduced is not limited to the angle described above. In addition, thepresent invention is not limited to the inference of the inventorsdescribed in the present specification.

In the following, the running stability in a case of performing therecording and/or reproducing of data by changing the head tilt angleduring the running of the magnetic tape in the high temperature and highhumidity environment is also simply referred to as “running stability”.In addition, the high temperature and high humidity environment can be,for example, an environment having a temperature of approximately 30° C.to 50° C. A humidity of the environment can be, for example,approximately 70% to 100% as a relative humidity. The temperatures andthe humidity described for the environment in the invention and thespecification are an atmosphere temperature and a relative humidity ofsuch an environment.

In the invention and the specification, the measurement of thefrictional force at each of the head tilt angles of 0°, 15°, 30°, and45° is performed by the following method in the environment with thetemperature of 32° C. and the relative humidity of 80%.

In addition, the head tilt angle for the frictional force measurement isan angle formed by an axis of the element array of the reproducingmodule of the LTO8 head with respect to a direction orthogonal to asliding direction in a first outward path of the following 100reciprocating slides. Such an angle is read as a direction orthogonal tothe sliding direction in FIG. 2 , and is an angle 0 formed by A and B.The head tilt angle is fixed during the 100 reciprocating slides.

The magnetic tape to be measured is placed on two cylindrical guiderolls having a diameter of 1 inch (1 inch=2.54 cm) spaced from eachother and arranged in parallel with each other so that the surface ofthe magnetic layer comes into contact therewith. In a randomly extractedportion of the magnetic tape to be measured, the surface of the magneticlayer of the magnetic tape is caused to slide on the LTO8 head with thehead tilt angle of 0°, 15°, 30°, or 45°, and a resistance forcegenerated during the sliding is detected by a strain gauge. Thereciprocating sliding is performed 100 times. For the measurementconditions, a lap angle θ is set to 6° and a sliding speed is set to 30mm/sec. A tension applied in the longitudinal direction of the magnetictape during the sliding is 0.55 N. Each sliding distance of the outwardpath and a return path is set to 5 cm. A dynamic frictional force in the100th outward path is set to the frictional force at each head tiltangle. During the measurement, one end of both ends of the magnetic tapeto be measured in the longitudinal direction is connected to the straingauge, and a tension of 0.20 N is applied to the other end thereof. Thefrictional force F value is calculated by the following equation, wherethe tension applied here is defined as To (unit: N) and the resistanceforce detected by the strain gauge is defined as T (unit: N). That is,here, the frictional force F is calculated as T₀=0.20. The measurementof the frictional forces F at the four head tilt angles is performed atdifferent parts of the magnetic tape to be measured in a random order.In addition, before each measurement, in order to be familiar with themeasurement environment, the magnetic tape to be measured is left on theguide roll as described above for 24 hours or longer. The standarddeviation (that is, a positive square root of the variance) iscalculated from the values of the frictional forces F at the four headtilt angles.F=T−T₀

Frictional Force F45° and Standard Deviation of Frictional Force F

Regarding the friction property of the magnetic tape, the frictionalforce F₄₅° is 4 gf to 15 gf, from a viewpoint of improving runningstability in a case of the recording and/or reproducing of data atdifferent head tilt angles in the high temperature and high humidityenvironment. From a viewpoint of further improving the runningstability, the frictional force F₄₅° is preferably 14 gf or less, morepreferably 13 gf, even more preferably 12 gf or less, and stillpreferably 11 gf or less. The frictional force F45. is 4 gf or more, andis preferably 5 gf or more, from a viewpoint of further improving therunning stability.

The standard deviation of the frictional force F on the magnetic layersurface with respect to the LTO8 head measured at each of head tiltangles 0°, 15°, 30°, and 45° is 10 gf or less, preferably 9 gf or less,more preferably 8 gf or less, even more preferably 7 gf or less, stillpreferably 6 gf or less, still more preferably 5 gf or less, and stilleven more preferably 4 gf or less, from a viewpoint of improving therunning stability in a case of performing the recording and/orreproducing at different head tilt angles in the high temperature andhigh humidity environment. The standard deviation can be, for example, 0gf or greater, greater than 0 gf, 1 gf or greater, or 2 gf or greater.It is preferable that the value of the standard deviation is small, froma viewpoint of further improving the running stability.

The friction property of the magnetic tape can be adjusted, for example,according to a kind of component used for manufacturing the magneticlayer. The details of this point will be described later.

Standard Deviation of Curvature

Next, a standard deviation of a curvature will be described.

The curvature of the magnetic tape in the longitudinal direction of thepresent invention and the present specification is a value obtained bythe following method in an environment of an atmosphere temperature of23° C. and a relative humidity of 50%. The magnetic tape is normallyaccommodated and circulated in a magnetic tape cartridge. As themagnetic tape to be measured, a magnetic tape taken out from an unusedmagnetic tape cartridge that is not attached to the magnetic tape deviceis used.

FIG. 4 is an explanatory diagram of the curvature of the magnetic tapein the longitudinal direction.

A tape sample having a length of 100 m in the longitudinal direction iscut out from a randomly selected portion of the magnetic tape to bemeasured. One end of this tape sample is defined as a position of 0 m,and a position spaced apart from this one end toward the other end by Dm (D meters) in the longitudinal direction is defined as a position of Dm. Accordingly, a position spaced apart by 10 m in the longitudinaldirection is defined as a position of 10 m, a position spaced apart by20 m is defined as a position of 20 m, and in this manner, a position of30 m, a position of 40 m, a position of 50 m, a position of 60 m, aposition of 70 m, a position of 80 m, a position of 90m, and a positionof 100 m are defined at intervals of 10 m sequentially.

A tape sample having a length of 1 m from the 0 m position to theposition of 1 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 0 m.

A tape sample having a length of 1 m from the 10 m position to theposition of 11 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 10 m.

A tape sample having a length of 1 m from the 20 m position to theposition of 21 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 20 m.

A tape sample having a length of 1 m from the 30 m position to theposition of 31 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 30 m.

A tape sample having a length of 1 m from the 40 m position to theposition of 41 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 40 m.

A tape sample having a length of 1 m from the 50 m position to theposition of 51 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 50 m.

A tape sample having a length of 1 m from the 60 m position to theposition of 61 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 60 m.

A tape sample having a length of 1 m from the 70 m position to theposition of 71 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 70 m.

A tape sample having a length of 1 m from the 80 m position to theposition of 81 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 80 m.

A tape sample having a length of 1 m from the 90 m position to theposition of 91 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 90 m.

A tape sample having a length of 1 m from the 99 m position to theposition of 100 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 100 m.

The tape sample of each position is hung for 24 hours±4 hours in atension-free state by gripping an upper end portion with a grippingmember (clip or the like) by setting the longitudinal direction as thevertical direction. Then, within 1 hour, the following measurement isperformed.

As shown in FIG. 4 , the tape piece is placed on a flat surface in atension-free state. The tape piece may be placed on a flat surface withthe surface on the magnetic layer side facing upward, or may be placedon a flat surface with the other surface facing upward. In FIG. 4 , Sindicates a tape sample and W indicates the width direction of the tapesample. Using an optical microscope, a distance L1 (unit: mm) that is ashortest distance between a virtual line 54 connecting both terminalportions 52 and 53 of the tape sample S and a maximum curved portion 55in the longitudinal direction of the tape sample S is measured. FIG. 4shows an example in which the tape sample is curved upward on a papersurface. Even in a case where the tape sample is curved downward, thedistance L1 (mm) is measured in the same manner. The distance L1 isdisplayed as a positive value regardless of which side is curved. In acase where no curve in the longitudinal direction is confirmed, the L1is set to 0 (zero) mm

By doing so, a standard deviation of the curvature L1 measured for atotal of 11 positions from the position of 0 m to the position of 100 m(that is, a positive square root of the dispersion) is the standarddeviation of the curvature of the magnetic tape to be measured in thelongitudinal direction (unit: mm/m).

In the magnetic tape, the standard deviation of the curvature obtainedby the method described above can be, for example, 7 mm/m or less and 6mm/m or less, and from a viewpoint of further improving the runningstability, it is preferably 5 mm/m or less, more preferably 4 mm/m orless, and even more preferably 3 mm/m or less. The standard deviation ofthe curvature of the magnetic tape can be, for example, 0 mm/m or more,more than 0 mm/m, 1 mm/m or more, or 2 mm/m or more. It is preferablethat the value of the standard deviation of the curvature is small, froma viewpoint of further improving the running stability. In addition, itis preferable that the value of the standard deviation of the curvatureis small, from a viewpoint of further improving the electromagneticconversion characteristics. From such a viewpoint, it is preferable thatthe standard deviation of the curvature is in the range described above.

The standard deviation of the curvature can be controlled by adjustingthe manufacturing conditions of the manufacturing step of the magnetictape. This point will be described later in detail.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder contained in the magnetic layer, awell-known ferromagnetic powder can be used as one kind or incombination of two or more kinds as the ferromagnetic powder used in themagnetic layer of various magnetic recording media. It is preferable touse a ferromagnetic powder having an average particle size as theferromagnetic powder, from a viewpoint of improvement of a recordingdensity. From this viewpoint, an average particle size of theferromagnetic powder is preferably equal to or smaller than 50 nm, morepreferably equal to or smaller than 45 nm, even more preferably equal toor smaller than 40 nm, further preferably equal to or smaller than 35nm, further more preferably equal to or smaller than 30 nm, further evenmore preferably equal to or smaller than 25 nm, and still preferablyequal to or smaller than 20 nm. Meanwhile, from a viewpoint of stabilityof magnetization, the average particle size of the ferromagnetic powderis preferably equal to or greater than 5 nm, more preferably equal to orgreater than 8 nm, even more preferably equal to or greater than 10 nm,still preferably equal to or greater than 15 nm, and still morepreferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is a ferromagnetic powder in which a hexagonal ferrite type crystalstructure is detected as a main phase by X-ray diffraction analysis. Themain phase is a structure to which a diffraction peak at the highestintensity in an X-ray diffraction spectrum obtained by the X-raydiffraction analysis belongs. For example, in a case where thediffraction peak at the highest intensity in the X-ray diffractionspectrum obtained by the X-ray diffraction analysis belongs to ahexagonal ferrite type crystal structure, it is determined that thehexagonal ferrite type crystal structure is detected as a main phase. Ina case where only a single structure is detected by the X-raydiffraction analysis, this detected structure is set as a main phase.The hexagonal ferrite type crystal structure includes at least an ironatom, a divalent metal atom, and an oxygen atom as constituting atoms. Adivalent metal atom is a metal atom which can be divalent cations asions, and examples thereof include an alkali earth metal atom such as astrontium atom, a barium atom, or a calcium atom, and a lead atom. Inthe invention and the specification, the hexagonal strontium ferritepowder is powder in which a main divalent metal atom included in thispowder is a strontium atom, and the hexagonal barium ferrite powder is apowder in which a main divalent metal atom included in this powder is abarium atom. The main divalent metal atom is a divalent metal atomoccupying the greatest content in the divalent metal atom included inthe powder based on atom %. However, the divalent metal atom describedabove does not include rare earth atom. The “rare earth atom” of theinvention and the specification is selected from the group consisting ofa scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. Thelanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europiumatom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosiumatom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom(Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspectof the hexagonal ferrite powder will be described more specifically.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1,600 nm³. The atomized hexagonalstrontium ferrite powder showing the activation volume in the rangedescribed above is suitable for manufacturing a magnetic tape exhibitingexcellent electromagnetic conversion characteristics. The activationvolume of the hexagonal strontium ferrite powder is preferably equal toor greater than 800 nm³, and can also be, for example, equal to orgreater than 850 nm³. In addition, from a viewpoint of further improvingthe electromagnetic conversion characteristics, the activation volume ofthe hexagonal strontium ferrite powder is more preferably equal to orsmaller than 1,500 nm³, even more preferably equal to or smaller than1,400 nm³, still preferably equal to or smaller than 1,300 nm³, stillmore preferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same applies to theactivation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an indexshowing a magnetic magnitude of the particles. Regarding the activationvolume and an anisotropy constant Ku which will be described laterdisclosed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using an oscillation sample typemagnetic-flux meter (measurement temperature: 23° C.±1° C.), and theactivation volume and the anisotropy constant Ku are values acquiredfrom the following relational expression of Hc and an activation volumeV. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[(kT/KuV)In(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rareearth atom. In a case where the hexagonal strontium ferrite powderincludes the rare earth atom, a content (bulk content) of the rare earthatom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of theiron atom. In one embodiment, the hexagonal strontium ferrite powderincluding the rare earth atom can have a rare earth atom surface layerportion uneven distribution. The “rare earth atom surface layer portionuneven distribution” of the invention and the specification means that acontent of rare earth atom with respect to 100 atom % of iron atom in asolution obtained by partially dissolving the hexagonal strontiumferrite powder with acid (hereinafter, referred to as a “rare earth atomsurface layer portion content” or simply a “surface layer portioncontent” regarding the rare earth atom) and a content of rare earth atomwith respect to 100 atom % of iron atom in a solution obtained bytotally dissolving the hexagonal strontium ferrite powder with acid(hereinafter, referred to as a “rare earth atom bulk content” or simplya “bulk content” regarding the rare earth atom) satisfy a ratio of rareearth atom surface layer portion content/rare earth atom bulk content>1.0.

The content of rare earth atom of the hexagonal strontium ferrite powderwhich will be described later is identical to the rare earth atom bulkcontent. With respect to this, the partial dissolving using acid is todissolve the surface layer portion of particles configuring thehexagonal strontium ferrite powder, and accordingly, the content of rareearth atom in the solution obtained by the partial dissolving is thecontent of rare earth atom in the surface layer portion of the particlesconfiguring the hexagonal strontium ferrite powder. The rare earth atomsurface layer portion content satisfying a ratio of “rare earth atomsurface layer portion content/rare earth atom bulk content >1.0” meansthat the rare earth atoms are unevenly distributed in the surface layerportion (that is, a larger amount of the rare earth atoms is present,compared to that inside), among the particles configuring the hexagonalstrontium ferrite powder. The surface layer portion of the invention andthe specification means a part of the region of the particlesconfiguring the hexagonal strontium ferrite powder towards the insidefrom the surface.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, a content (bulk content) of the rare earth atom ispreferably in a range of 0.5 to 5.0 atom % with respect to 100 atom % ofthe iron atom. It is thought that the rare earth atom having the bulkcontent in the range described above and uneven distribution of the rareearth atom in the surface layer portion of the particles configuring thehexagonal strontium ferrite powder contribute to the prevention of adecrease in reproducing output during the repeated reproducing. It issurmised that this is because the rare earth atom having the bulkcontent in the range described above included in the hexagonal strontiumferrite powder and the uneven distribution of the rare earth atom in thesurface layer portion of the particles configuring the hexagonalstrontium ferrite powder can increase the anisotropy constant Ku. As thevalue of the anisotropy constant Ku is high, occurrence of a phenomenoncalled thermal fluctuation (that is, improvement of thermal stability)can be prevented. By preventing the occurrence of the thermalfluctuation, a decrease in reproducing output during the repeatedreproducing can be prevented. It is surmised that the unevendistribution of the rare earth atom in the surface layer portion of theparticles of the hexagonal strontium ferrite powder contributes tostabilization of a spin at an iron (Fe) site in a crystal lattice of thesurface layer portion, thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontiumferrite powder having the rare earth atom surface layer portion unevendistribution as the ferromagnetic powder of the magnetic layer alsocontributes to the prevention of chipping of the surface of the magneticlayer due to the sliding with the magnetic head. That is, it is surmisedthat, the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution can also contribute to theimprovement of running durability of the magnetic tape. It is surmisedthat this is because the uneven distribution of the rare earth atom onthe surface of the particles configuring the hexagonal strontium ferritepowder contributes to improvement of an interaction between the surfaceof the particles and an organic substance (for example, binding agentand/or additive) included in the magnetic layer, thereby improvinghardness of the magnetic layer.

From a viewpoint of preventing reduction of the reproduction output inthe repeated reproduction and/or a viewpoint of further improvingrunning durability, the content of rare earth atom (bulk content) ismore preferably in a range of 0.5 to 4.5 atom %, even more preferably ina range of 1.0 to 4.5 atom %, and still preferably in a range of 1.5 to4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder including therare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atoms are included, thebulk content is obtained from the total of the two or more kinds of rareearth atoms. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of preventing reduction of the reproduction outputduring the repeated reproduction include a neodymium atom, a samariumatom, an yttrium atom, and a dysprosium atom, a neodymium atom, asamarium atom, an yttrium atom are more preferable, and a neodymium atomis even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution, a degree of unevendistribution of the rare earth atom is not limited, as long as the rareearth atom is unevenly distributed in the surface layer portion of theparticles configuring the hexagonal strontium ferrite powder. Forexample, regarding the hexagonal strontium ferrite powder having therare earth atom surface layer portion uneven distribution, a ratio ofthe surface layer portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions which willbe described later and the bulk content of the rare earth atom obtainedby total dissolving performed under the dissolving conditions which willbe described later, “surface layer portion content/bulk content” isgreater than 1.0 and can be equal to or greater than 1.5. The “surfacelayer portion content/bulk content” greater than 1.0 means that the rareearth atoms are unevenly distributed in the surface layer portion (thatis, a larger amount of the rare earth atoms is present, compared to thatinside), in the particles configuring the hexagonal strontium ferritepowder. A ratio of the surface layer portion content of the rare earthatom obtained by partial dissolving performed under the dissolvingconditions which will be described later and the bulk content of therare earth atom obtained by total dissolving performed under thedissolving conditions which will be described later, “surface layerportion content/bulk content” can be, for example, equal to or smallerthan 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0,equal to or smaller than 7.0, equal to or smaller than 6.0, equal to orsmaller than 5.0, or equal to or smaller than 4.0. However, in thehexagonal strontium ferrite powder having the rare earth atom surfacelayer portion uneven distribution, the “surface layer portioncontent/bulk content” is not limited to the exemplified upper limit orthe lower limit, as long as the rare earth atom is unevenly distributedin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by,for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed in a case of the completion of the dissolving. For example, byperforming the partial dissolving, a region of the particles configuringthe hexagonal strontium ferrite powder which is 10% to 20% by mass withrespect to 100% by mass of a total of the particles can be dissolved. Onthe other hand, the total dissolving means dissolving performed untilthe hexagonal strontium ferrite powder remaining in the solution is notvisually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 nm. The element analysis of the filtrate obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface layer portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface layer portion content. The same applies to the measurement ofthe bulk content.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface layer portion content, and the bulkcontent with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regards to this point, in hexagonal strontium ferritepowder which includes the rare earth atom but does not have the rareearth atom surface layer portion uneven distribution, us tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it isthought that, hexagonal strontium ferrite powder having the rare earthatom surface layer portion uneven distribution is also preferable forpreventing such a significant decrease in us. In one aspect, us of thehexagonal strontium ferrite powder can be equal to or greater than 45A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On theother hand, from a viewpoint of noise reduction, us is preferably equalto or smaller than 80 A×m²/kg and more preferably equal to or smallerthan 60 A×m²/kg. us can be measured by using a well-known measurementdevice capable of measuring magnetic properties such as an oscillationsample type magnetic-flux meter. In the invention and the specification,the mass magnetization us is a value measured at a magnetic fieldstrength of 15 kOe, unless otherwise noted.

Regarding the content (bulk content) of the constituting atom in thehexagonal strontium ferrite powder, a content of the strontium atom canbe, for example, in a range of 2.0 to 15.0 atom % with respect to 100atom % of the iron atom. In one aspect, in the hexagonal strontiumferrite powder, the divalent metal atom included in this powder can beonly a strontium atom. In another aspect, the hexagonal strontiumferrite powder can also include one or more kinds of other divalentmetal atoms, in addition to the strontium atom. For example, thehexagonal strontium ferrite powder can include a barium atom and/or acalcium atom. In a case where the other divalent metal atom other thanthe strontium atom is included, a content of a barium atom and a contentof a calcium atom in the hexagonal strontium ferrite powder respectivelycan be, for example, in a range of 0.05 to 5.0 atom % with respect to100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one aspect, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, and an oxygen atom, and can also includea rare earth atom. In addition, the hexagonal strontium ferrite powdermay or may not include atoms other than these atoms. As an example, thehexagonal strontium ferrite powder may include an aluminum atom (Al). Acontent of the aluminum atom can be, for example, 0.5 to 10.0 atom %with respect to 100 atom % of the iron atom. From a viewpoint ofpreventing the reduction of the reproduction output during the repeatedreproduction, the hexagonal strontium ferrite powder includes the ironatom, the strontium atom, the oxygen atom, and the rare earth atom, anda content of the atoms other than these atoms is preferably equal to orsmaller than 10.0 atom %, more preferably in a range of 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, in one aspect, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting a value of the content (unit: % by mass)of each atom obtained by totally dissolving the hexagonal strontiumferrite powder into a value shown as atom % by using the atomic weightof each atom. In addition, in the invention and the specification, agiven atom which is “not included” means that the content thereofobtained by performing total dissolving and measurement by using an ICPanalysis device is 0% by mass. A detection limit of the ICP analysisdevice is generally equal to or smaller than 0.01 ppm (parts permillion) based on mass. The expression “not included” is used as ameaning including that a given atom is included with the amount smallerthan the detection limit of the ICP analysis device. In one aspect, thehexagonal strontium ferrite powder does not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

E-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-ironoxide type crystal structure is detected as a main phase by X-raydiffraction analysis. For example, in a case where the diffraction peakat the highest intensity in the X-ray diffraction spectrum obtained bythe X-ray diffraction analysis belongs to an ε-iron oxide type crystalstructure, it is determined that the ε-iron oxide type crystal structureis detected as a main phase. As a manufacturing method of the ε-ironoxide powder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. For the method of manufacturing the ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. 51, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp.5200-5206 can be referred, for example. However, themanufacturing method of the ε-iron oxide powder capable of being used asthe ferromagnetic powder in the magnetic layer of the magnetic tape isnot limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably in a rangeof 300 to 1,500 nm³. The atomized ε-iron oxide powder showing theactivation volume in the range described above is suitable formanufacturing a magnetic tape exhibiting excellent electromagneticconversion characteristics. The activation volume of the ε-iron oxidepowder is preferably equal to or greater than 300 nm³, and can also be,for example, equal to or greater than 500 nm³. In addition, from aviewpoint of further improving the electromagnetic conversioncharacteristics, the activation volume of the ε-iron oxide powder ismore preferably equal to or smaller than 1,400 nm³, even more preferablyequal to or smaller than 1,300 nm³, still preferably equal to or smallerthan 1,200 nm³, and still more preferably equal to or smaller than 1,100nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regard to this point, in one aspect, σs of the ε-ironoxide powder can be equal to or greater than 8 A×m²/kg and can also beequal to or greater than 12 A×m²/kg. On the other hand, from a viewpointof noise reduction, σs of the ε-iron oxide powder is preferably equal toor smaller than 40 A×m²/kg and more preferably equal to or smaller than35 A×m²/kg.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with atransmission electron microscope, the image is printed on photographicprinting paper or displayed on a display so that the total magnificationratio of 500,000 to obtain an image of particles configuring the powder.A target particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetic mean of the particle size of 500particles obtained as described above is the average particle size ofthe powder. As the transmission electron microscope, a transmissionelectron microscope H-9000 manufactured by Hitachi, Ltd. can be used,for example. In addition, the measurement of the particle size can beperformed by a well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an aspect in which particles configuring theaggregate are directly in contact with each other, but also includes anaspect in which a binding agent or an additive which will be describedlater is interposed between the particles. A term, particles may be usedfor representing the powder.

As a method for collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

(1) in a case where the shape of the particle observed in the particleimage described above is a needle shape, a fusiform shape, or a columnarshape (here, a height is greater than a maximum long diameter of abottom surface), the size (particle size) of the particles configuringthe powder is shown as a length of a major axis configuring theparticle, that is, a major axis length,

(2) in a case where the shape of the particle is a planar shape or acolumnar shape (here, a thickness or a height is smaller than a maximumlong diameter of a plate surface or a bottom surface), the particle sizeis shown as a maximum long diameter of the plate surface or the bottomsurface, and

(3) in a case where the shape of the particle is a sphere shape, apolyhedron shape, or an unspecified shape, and the major axisconfiguring the particles cannot be specified from the shape, theparticle size is shown as an equivalent circle diameter. The equivalentcircle diameter is a value obtained by a circle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a minor axis, that is, a minor axis length of the particles ismeasured in the measurement described above, a value of (major axislength/minor axis length) of each particle is obtained, and anarithmetic mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the minoraxis length as the definition of the particle size is a length of aminor axis configuring the particle, in a case of (2), the minor axislength is a thickness or a height, and in a case of (3), the major axisand the minor axis are not distinguished, thus, the value of (major axislength/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average major axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably in a range of 50% to 90% by mass and morepreferably in a range of 60% to 90% by mass with respect to a total massof the magnetic layer. A high filling percentage of the ferromagneticpowder in the magnetic layer is preferable from a viewpoint ofimprovement of recording density.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include abinding agent in the magnetic layer. The binding agent is one or morekinds of resin. As the binding agent, various resins normally used as abinding agent of a coating type magnetic recording medium can be used.As the binding agent, a resin selected from a polyurethane resin, apolyester resin, a polyamide resin, a vinyl chloride resin, an acrylicresin obtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later. For thebinding agent described above, descriptions disclosed in paragraphs 0028to 0031 of JP2010-24113A can be referred to. In addition, the bindingagent may be a radiation curable resin such as an electron beam curableresin. For the radiation curable resin, paragraphs 0044 and 0045 ofJP2011-048878A can be referred to.

An average molecular weight of the resin used as the binding agent canbe, for example, 10,000 to 200,000 as a weight-average molecular weight.The amount of the binding agent used can be, for example, 1.0 to 30.0parts by mass with respect to 100.0 parts by mass of the ferromagneticpowder.

Curing Agent

A curing agent can also be used together with the binding agent. As thecuring agent, in one aspect, a thermosetting compound which is acompound in which a curing reaction (crosslinking reaction) proceeds dueto heating can be used, and in another aspect, a photocurable compoundin which a curing reaction (crosslinking reaction) proceeds due to lightirradiation can be used. At least a part of the curing agent is includedin the magnetic layer in a state of being reacted (crosslinked) withother components such as the binding agent, by proceeding the curingreaction in the manufacturing step of the magnetic tape. The preferredcuring agent is a thermosetting compound, and polyisocyanate issuitable. For the details of polyisocyanate, descriptions disclosed inparagraphs 0124 and 0125 of JP2011-216149A can be referred to. Theamount of the curing agent can be, for example, 0 to 80.0 parts by masswith respect to 100.0 parts by mass of the binding agent in the magneticlayer forming composition, and is preferably 50.0 to 80.0 parts by mass,from a viewpoint of improvement of hardness of each layer such as themagnetic layer.

Other Components

The magnetic layer may include one or more kinds of additives, asnecessary. As the additives, a commercially available product can besuitably selected and used according to the desired properties.Alternatively, a compound synthesized by a well-known method can be usedas the additives. As the additives, the curing agent described above isused as an example. In addition, examples of the additive included inthe magnetic layer include a non-magnetic filler, a lubricant, adispersing agent, a dispersing assistant, an antibacterial agent, anantistatic agent, and an antioxidant. The non-magnetic filler isidentical to the non-magnetic particles or non-magnetic powder. As thenon-magnetic filler, a non-magnetic filler which can function as aprojection formation agent and a non-magnetic filler which can functionas an abrasive can be used. As the additive, a well-known additive suchas various polymers disclosed in paragraphs 0030 to 0080 ofJP2016-051493A can also be used.

As the projection formation agent which is one aspect of thenon-magnetic filler, particles of an inorganic substance can be used,particles of an organic substance can be used, and composite particlesof the inorganic substance and the organic substance can also be used.In addition, carbon black can also be used. Examples of the inorganicsubstance include inorganic oxide such as metal oxide, metal carbonate,metal sulfate, metal nitride, metal carbide, and metal sulfide, andinorganic oxide is preferable. In one aspect, the projection formationagent can be inorganic oxide-based particles. Here, “-based” means“-containing”. One aspect of the inorganic oxide-based particles isparticles consisting of inorganic oxide. Another aspect of the inorganicoxide-based particles is composite particles of inorganic oxide and anorganic substance, and as a specific example, composite particles ofinorganic oxide and a polymer can be used. As such particles, forexample, particles obtained by binding a polymer to a surface of theinorganic oxide particle can be used.

An average particle size of the projection formation agent can be, forexample, 30 to 300 nm and is preferably 40 to 200 nm. In addition,regarding a shape of the projection formation agent, it is consideredthat the closer the shape of the projection formation agent particlescontained in the magnetic layer is to a true sphere, the more likely thefriction property tends to change due to a difference in head tiltangle. This is due to the following reasons. In a case where the headtilt angle is different, a contact state between the LTO8 head and thesurface of the magnetic layer of the magnetic tape in a case ofmeasuring the frictional force can change, and accordingly, a pressureapplied to the surface of the magnetic layer due to the contact with theLTO8 head can also change. It is considered that the closer the shape ofthe particle is to a true sphere, the smaller an indentation resistancethat exerts in a case where pressure is applied, and accordingly, theparticles are likely to be affected by the change in pressure. Withrespect to this, it is surmised that, in a case where the shape of theparticles is a shape other than the sphere, for example, a shape of aso-called deformed shape, a large indentation resistance is easilyexerted, in a case where the pressure is applied, and accordingly,particles tends to be not likely to be affected by the change inpressure. In addition, it is considered that even particles having aninhomogeneous particle surface and low surface smoothness tend to be notlikely to be affected by the change in pressure, because a largeindentation resistance tends to exert in a case where the pressure isapplied. Therefore, the inventors consider that, the usage of theprojection formation agent whose particle shape is a shape other thanthe sphere and/or the usage of the projection formation agent having aninhomogeneous particle surface and low surface smoothness can contributeto making the frictional force of F45° and the standard deviation of thefrictional force F be in the ranges described above, respectively. Inaddition, in one embodiment, a projection formation agent having aso-called unspecified shape can be used as the projection formationagent.

The abrasive which is another aspect of the non-magnetic filler ispreferably a non-magnetic powder having Mohs hardness exceeding 8 andmore preferably a non-magnetic powder having Mohs hardness equal to orgreater than 9. With respect to this, the Mohs hardness of theprojection formation agent can be, for example, equal to or smaller than8 or equal to or smaller than 7. A maximum value of Mohs hardness is 10of diamond. Specific examples of the abrasive include powders of alumina(for example, Al₂O₃), silicon carbide, boron carbide (for example, B₄C),SiO₂, TiC, chromium oxide (Cr₂O₃), cerium oxide, zirconium oxide (forexample, ZrO₂), iron oxide, diamond, and the like, and among these,alumina powder such as a-alumina and silicon carbide powder arepreferable. In addition, an average particle size of the abrasive canbe, for example, in a range of 30 to 300 nm and is preferably in a rangeof 50 to 200 nm.

From a viewpoint of causing the projection formation agent and theabrasive to exhibit these functions in more excellent manner, a contentof the projection formation agent in the magnetic layer is preferably0.1 to 4.0 parts by mass, more preferably 0.3 to 3.5 parts by mass, andeven more preferably 0.5 to 2.5 parts by mass with respect to 100.0parts by mass of the ferromagnetic powder. Meanwhile, a content of theabrasive in the magnetic layer is preferably 1.0 to 20.0 parts by mass,more preferably 3.0 to 15.0 parts by mass, and even more preferably 4.0to 10.0 parts by mass, with respect to 100.0 parts by mass of theferromagnetic powder.

As an example of the additive which can be used in the magnetic layerincluding the abrasive, a dispersing agent disclosed in paragraphs 0012to 0022 of JP2013-131285A can be used as a dispersing agent forimproving dispersibility of the abrasive in the magnetic layer formingcomposition. In addition, for the dispersing agent, a descriptiondisclosed in paragraphs 0061 and 0071 of JP2012-133837A can be referredto. The dispersing agent may be included in the non-magnetic layer. Forthe dispersing agent which may be included in the non-magnetic layer, adescription disclosed in a paragraph 0061 of JP2012-133837A can bereferred to.

In addition, as an aspect of an additive that can be contained in themagnetic layer, a compound having an ammonium salt structure of an alkylester anion represented by Formula 1 can be used.

(In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms, and Z⁺represents an ammonium cation.)

The present inventors consider that the compound described above canfunction as a lubricant. This will be described in detail below.

The lubricant can be broadly divided into a fluid lubricant and aboundary lubricant. The inventors consider that a compound having anammonium salt structure of an alkyl ester anion represented by Formula 1can function as a fluid lubricant. It is considered that the fluidlubricant can play a role of imparting lubricity to the magnetic layerby forming a liquid film on the surface of the magnetic layer by itself.It is surmised that, in order to control the frictional force F₄₅° andthe standard deviation of the frictional force F, it is desirable thatthe fluid lubricant forms a liquid film on the surface of the magneticlayer. In addition, the more stably the surface of the magnetic layerand the LTO8 head can slide in a case of measuring the frictional force,the smaller the values of the frictional force F₄₅° and the standarddeviation of the frictional force F can be. Regarding the liquid film ofthe fluid lubricant, from a viewpoint of enabling more stable sliding,it is considered that it is desirable to use an appropriate amount ofthe fluid lubricant which forms the liquid film on the surface of themagnetic layer. This is because it is surmised that, in a case where theamount of the liquid lubricant which forms the liquid film on thesurface of the magnetic layer is excessive, the surface of the magneticlayer and the LTO8 head stick to each other, and the sliding stabilitytends to decrease. In addition, it is surmised that, in a case where theamount of the liquid lubricant which forms the liquid film on thesurface of the magnetic layer is excessive, the projection formed on thesurface of the magnetic layer by, for example, the non-magnetic filleris covered with the liquid film. It is considered that this can also bea factor that decreases the sliding stability.

With respect to the point described above, the compound described abovehas an ammonium salt structure of an alkyl ester anion represented byFormula 1. It is considered that the compound having such a structurecan play an excellent role as the fluid lubricant even in a relativelysmall amount. Therefore, it is considered that including the compounddescribed above in the magnetic layer leads to improving the slidingstability between the surface of the magnetic layer of the magnetic tapeand the LTO8 head, and contributes to controlling the frictional forceF₄₅° and the standard deviation of the frictional force F.

Hereinafter, the compound will be further described in detail.

In the invention and the specification, unless otherwise noted, groupsdescribed may have a substituent or may be unsubstituted. In addition,the “number of carbon atoms” of a group having a substituent means thenumber of carbon atoms not including the number of carbon atoms of thesubstituent, unless otherwise noted. In the present invention and thespecification, examples of the substituent include an alkyl group (forexample, an alkyl group having 1 to 6 carbon atoms), a hydroxy group, analkoxy group (for example, an alkoxy group having 1 to 6 carbon atoms),a halogen atom (for example, a fluorine atom, a chlorine atom, a bromineatom, or the like), a cyano group, an amino group, a nitro group, anacyl group, a carboxy group, salt of a carboxy group, a sulfonic acidgroup, and salt of a sulfonic acid group.

Regarding the compound having an ammonium salt structure of the alkylester anion represented by the formula 1, at least a part thereofincluded in the magnetic layer can form a liquid film on the surface ofthe magnetic layer, and another part thereof can be included in themagnetic layer, move to the surface of the magnetic layer and form theliquid film during the sliding with the magnetic head. In addition,still another part thereof can be included in the non-magnetic layerwhich will be described later, and can move to the magnetic layer,further move to the surface of the magnetic layer, and form a liquidfilm. The “alkyl ester anion” can also be referred to as an “alkylcarboxylate anion”.

In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms. Thefluorinated alkyl group has a structure in which some or all of thehydrogen atoms constituting the alkyl group are substituted with afluorine atom. The alkyl group or fluorinated alkyl group represented byR may have a linear structure, a branched structure, may be a cyclicalkyl group or fluorinated alkyl group, and preferably has a linearstructure. The alkyl group or fluorinated alkyl group represented by Rmay have a substituent, may be unsubstituted, and is preferablyunsubstituted. The alkyl group represented by R can be represented by,for example, C_(n)H_(2n+1)-. Here, n represents an integer of 7 or more.In addition, for example, the fluorinated alkyl group represented by Rmay have a structure in which a part or all of the hydrogen atomsconstituting the alkyl group represented by C_(n)H_(2n+1)-. aresubstituted with a fluorine atom. The alkyl group or fluorinated alkylgroup represented by R has 7 or more carbon atoms, preferably 8 or morecarbon atoms, more preferably 9 or more carbon atoms, further preferably10 or more carbon atoms, still preferably 11 or more carbon atoms, stillmore preferably 12 or more carbon atoms, and still even more preferably13 or more carbon atoms. The alkyl group or fluorinated alkyl grouprepresented by R has preferably 20 or less carbon atoms, more preferably19 or less carbon atoms, and even more preferably 18 or less carbonatoms.

In Formula 1, Z⁺ represents an ammonium cation. Specifically, theammonium cation has the following structure. In the present inventionand the present specification, “*” in the formulas that represent a partof the compound represents a bonding position between the structure ofthe part and the adjacent atom.

The nitrogen cation N⁺ of the ammonium cation and the oxygen anion O⁻ inFormula 1 may form a salt bridging group to form the ammonium saltstructure of the alkyl ester anion represented by Formula 1. The factthat the compound having the ammonium salt structure of the alkyl esteranion represented by Formula 1 is contained in the magnetic layer can beconfirmed by performing analysis with respect to the magnetic tape byX-ray photoelectron spectroscopy (electron spectroscopy for chemicalanalysis (ESCA)), infrared spectroscopy (IR), or the like.

In one embodiment, the ammonium cation represented by Z⁺ can be providedby, for example, the nitrogen atom of the nitrogen-containing polymerbecoming a cation. The nitrogen-containing polymer means a polymercontaining a nitrogen atom. In the present invention and the presentspecification, a term “polymer” means to include both a homopolymer anda copolymer. The nitrogen atom can be included as an atom configuring amain chain of the polymer in one aspect, and can be included as an atomconstituting a side chain of the polymer in one aspect.

As one aspect of the nitrogen-containing polymer, polyalkyleneimine canbe used. The polyalkyleneimine is a ring-opening polymer ofalkyleneimine and is a polymer having a plurality of repeating unitsrepresented by Formula 2.

The nitrogen atom N configuring the main chain in Formula 2 can beconverted to a nitrogen cation N⁺ to provide an ammonium cationrepresented by Z⁺ in Formula 1. Then, an ammonium salt structure can beformed with the alkyl ester anion, for example, as follows.

Hereinafter, Formula 2 will be described in more detail.

In Formula 2, R¹ and R² each independently represent a hydrogen atom oran alkyl group, and n1 represents an integer of 2 or more.

Examples of the alkyl group represented by R¹ or R² include an alkylgroup having 1 to 6 carbon atoms, preferably an alkyl group having 1 to3 carbon atoms, more preferably a methyl group or an ethyl group, andeven more preferably a methyl group. The alkyl group represented by R¹or R² is preferably an unsubstituted alkyl group. A combination of R¹and R² in Formula 2 is a form in which one is a hydrogen atom and theother is an alkyl group, a form in which both are hydrogen atoms, and aform in which both are an alkyl group (the same or different alkylgroups), and is preferably a form in which both are hydrogen atoms. Asthe alkyleneimine that provides the polyalkyleneimine, a structure ofthe ring that has the smallest number of carbon atoms is ethyleneimine,and the main chain of the alkyleneimine (ethyleneimine) obtained by ringopening of ethyleneimine has 2 carbon atoms. Accordingly, n1 in Formula2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 orless, 6 or less, or 4 or less. The polyalkyleneimine may be ahomopolymer containing only the same structure as the repeatingstructure represented by Formula 2, or may be a copolymer containing twoor more different structures as the repeating structure represented byFormula 2. A number average molecular weight of the polyalkyleneiminethat can be used to form the compound having the ammonium salt structureof the alkyl ester anion represented by Formula 1 can be, for example,equal to or greater than 200, and is preferably equal to or greater than300, and more preferably equal to or greater than 400. In addition, thenumber average molecular weight of the polyalkyleneimine can be, forexample, equal to or less than 10,000, and is preferably equal to orless than 5,000 and more preferably equal to or less than 2,000.

In the present invention and the present specification, the averagemolecular weight (weight-average molecular weight and number averagemolecular weight) is measured by gel permeation chromatography (GPC) andis a value obtained by performing standard polystyrene conversion.Unless otherwise noted, the average molecular weights shown in theexamples which will be described below are values(polystyrene-equivalent values) obtained by standard polystyreneconversion of the values measured under the following measurementconditions using GPC.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard Column TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three kinds of columns are linked in series)

Eluent: Tetrahydrofuran (THF), including stabilizer(2,6-di-t-butyl-4-methylphenol)

Eluent flow rate: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3% by mass

Sample injection amount: 10 μL

In addition, as the other aspect of the nitrogen-containing polymer,polyallylamine can be used. The polyallylamine is a polymer ofallylamine and is a polymer having a plurality of repeating unitsrepresented by Formula 3.

The nitrogen atom N configuring an amino group of a side chain inFormula 3 can be converted to a nitrogen cation N⁺ to provide anammonium cation represented by Z⁺ in Formula 1. Then, an ammonium saltstructure can be formed with the alkyl ester anion, for example, asfollows.

A weight-average molecular weight of the polyallylamine that can be usedto form the compound having the ammonium salt structure of the alkylester anion represented by Formula 1 can be, for example, equal to orgreater than 200, and is preferably equal to or greater than 1,000, andmore preferably equal to or greater than 1,500. In addition, theweight-average molecular weight of the polyallylamine can be, forexample, equal to or less than 15,000, and is preferably equal to orless than 10,000 and more preferably equal to or less than 8,000.

The fact that the compound having a structure derived frompolyalkyleneimine or polyallylamine as the compound having the ammoniumsalt structure of the alkyl ester anion represented by Formula 1 isincluded can be confirmed by analyzing the surface of the magnetic layerby a time-of-flight secondary ion mass spectrometry (TOF-SIMS) or thelike.

The compound having the ammonium salt structure of the alkyl ester anionrepresented by Formula 1 can be salt of a nitrogen-containing polymerand one or more fatty acids selected from the group consisting of fattyacids having 7 or more carbon atoms and fluorinated fatty acids having 7or more carbon atoms. The nitrogen-containing polymer forming salt canbe one kind or two or more kinds of nitrogen-containing polymers, andcan be, for example, a nitrogen-containing polymer selected from thegroup consisting of polyalkyleneimine and polyallylamine The fatty acidsforming the salt can be one kind or two or more kinds of fatty acidsselected from the group consisting of fatty acids having 7 or morecarbon atoms and fluorinated fatty acids having 7 or more carbon atoms.The fluorinated fatty acid has a structure in which some or all of thehydrogen atoms configuring the alkyl group bonded to a carboxy groupCOOH in the fatty acid are substituted with fluorine atoms. For example,the salt forming reaction can easily proceed by mixing thenitrogen-containing polymer and the fatty acids described above at roomtemperature. The room temperature is, for example, approximately 20° C.to 25° C. In one embodiment, one or more kinds of nitrogen-containingpolymers and one or more kinds of the fatty acids described above areused as components of the magnetic layer forming composition, and thesalt forming reaction can proceed by mixing these in the step ofpreparing the magnetic layer forming composition. In one embodiment, oneor more kinds of nitrogen-containing polymers and one or more kinds ofthe fatty acids described above are mixed to form a salt beforepreparing the magnetic layer forming composition, and then, the magneticlayer forming composition can be prepared using this salt as a componentof the magnetic layer forming composition. This point also applies to acase of forming a non-magnetic layer including a compound having anammonium salt structure of an alkyl ester anion represented byFormula 1. For example, for the magnetic layer, 0.1 to 10.0 parts bymass of the nitrogen-containing polymer can be used and 0.5 to 8.0 partsby mass of the nitrogen-containing polymer is preferably used withrespect to 100.0 parts by mass of ferromagnetic powder. The used amountof the fatty acids described above can be, for example, 0.05 to 10.0parts by mass and is preferably 0.1 to 5.0 parts by mass, with respectto 100.0 parts by mass of ferromagnetic powder. In addition, for thenon-magnetic layer, 0.1 to 10.0 parts by mass of the nitrogen-containingpolymer can be used and 0.5 to 8.0 parts by mass of thenitrogen-containing polymer is preferably used with respect to 100.0parts by mass of non-magnetic powder. The used amount of the fatty acidsdescribed above can be, for example, 0.05 to 10.0 parts by mass and ispreferably 0.1 to 5.0 parts by mass, with respect to 100.0 parts by massof non-magnetic powder. In a case where the nitrogen-containing polymerand the fatty acid are mixed to form an ammonium salt of the alkyl esteranion represented by Formula 1, the nitrogen atom configuring thenitrogen-containing polymer and the carboxy group of the fatty acid maybe reacted to form the following structure, and a form including suchstructures are also included in the above compound.

Examples of the fatty acids include fatty acids having an alkyl groupdescribed above as R in Formula 1 and fluorinated fatty acids having afluorinated alkyl group described above as R in Formula 1.

A mixing ratio of the nitrogen-containing polymer and the fatty acidused to form the compound having the ammonium salt structure of thealkyl ester anion represented by Formula 1 is preferably 10:90 to 90:10,more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20,as a mass ratio of nitrogen-containing polymer:fatty acid. In addition,the compound having the ammonium salt structure of the alkyl ester anionrepresented by Formula 1 that is contained in the magnetic layer ispreferably 0.01 parts by mass or more, more preferably 0.1 parts bymass, even more preferably 0.5 parts by mass with respect to 100.0 partsby mass of the ferromagnetic powder. Here, a content of the compound inthe magnetic layer means a total amount of the amount of the liquid filmformed on the surface of the magnetic layer and the amount contained inthe magnetic layer. On the other hand, it is preferable that a contentof the ferromagnetic powder in the magnetic layer is high from aviewpoint of high-density recording. Therefore, from a viewpoint ofhigh-density recording, it is preferable that a content of componentsother than the ferromagnetic powder is small. From this viewpoint, thecontent of the compound in the magnetic layer is preferably 15.0 partsby mass or less, more preferably 10.0 parts by mass or less, and evenmore preferably 8.0 parts by mass or less with respect to 100.0 parts bymass of the ferromagnetic powder. In addition, the same applies to thepreferable range of the content of the compound in the magnetic layerforming composition used for forming the magnetic layer.

As the lubricant, for example, a fatty acid amide that can function as aboundary lubricant can be used. It is considered that the boundarylubricant is a lubricant which can be adsorbed to a surface of powder(for example, ferromagnetic powder) and form a rigid lubricant film todecrease contact friction. Examples of fatty acid amide include amide ofvarious fatty acids such as lauric acid, myristic acid, palmitic acid,stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid,erucic acid, and elaidic acid, and specifically, lauric acid amide,myristic acid amide, palmitic acid amide, stearic acid amide, and thelike. The content of fatty acid amide in the magnetic layer is, forexample, 0 to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, andmore preferably 0 to 1.0 parts by mass with respect to 100.0 parts bymass of the ferromagnetic powder. In addition, the non-magnetic layermay also contain fatty acid amide. The content of fatty acid amide inthe non-magnetic layer is, for example, 0 to 3.0 parts by mass and ispreferably 0 to 1.0 parts by mass with respect to 100.0 parts by mass ofnon-magnetic powder. For the dispersing agent, a description disclosedin paragraphs 0061 and 0071 of JP2012-133837A can be referred to. Thedispersing agent may be added to a non-magnetic layer formingcomposition. For the dispersing agent which can be added to thenon-magnetic layer forming composition, a description disclosed inparagraph 0061 of JP2012-133837A can be referred to.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the non-magnetic support or mayinclude a non-magnetic layer containing the non-magnetic powder betweenthe non-magnetic support and the magnetic layer. The non-magnetic powderused for the non-magnetic layer may be a powder of an inorganicsubstance (inorganic powder) or a powder of an organic substance(organic powder). In addition, carbon black and the like can be used.Examples of the inorganic substance include metal, metal oxide, metalcarbonate, metal sulfate, metal nitride, metal carbide, and metalsulfide. The non-magnetic powder can be purchased as a commerciallyavailable product or can be manufactured by a well-known method. Fordetails thereof, descriptions disclosed in paragraphs 0146 to 0150 ofJP2011-216149A can be referred to. For carbon black which can be used inthe non-magnetic layer, descriptions disclosed in paragraphs 0040 and0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably in a range of 50% to 90% by mass and more preferably in arange of 60% to 90% by mass with respect to a total mass of thenon-magnetic layer.

The non-magnetic layer can include a binding agent and can also includeadditives. In regards to other details of a binding agent or additivesof the non-magnetic layer, the well-known technology regarding thenon-magnetic layer can be applied. In addition, in regards to the typeand the content of the binding agent, and the type and the content ofthe additive, for example, the well-known technology regarding themagnetic layer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer containing a small amount offerromagnetic powder as impurities, or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heat treatmentmay be performed with respect to these supports in advance.

Back Coating Layer

The tape may or may not include a back coating layer containing anon-magnetic powder on a surface side of the non-magnetic supportopposite to the surface side provided with the magnetic layer. The backcoating layer preferably includes any one or both of carbon black andinorganic powder. The back coating layer can include a binding agent andcan also include additives. For the details of the non-magnetic powder,the binding agent included in the back coating layer and variousadditives, a well-known technology regarding the back coating layer canbe applied, and a well-known technology regarding the magnetic layerand/or the non-magnetic layer can also be applied. For example, for theback coating layer, descriptions disclosed in paragraphs 0018 to 0020 ofJP2006-331625A and page 4, line 65, to page 5, line 38, of US7029774Bcan be referred to.

Various Thicknesses

Regarding a tape thickness (total thickness) of the magnetic tape, ithas been required to increase recording capacity (increase in capacity)of the magnetic tape along with the enormous increase in amount ofinformation in recent years. As a unit for increasing the capacity, atape thickness of the magnetic tape is reduced and a length of themagnetic tape accommodated in one reel of the magnetic tape cartridge isincreased. From this point, the tape thickness of the magnetic tape ispreferably 5.6 μm or less, more preferably 5.5 μm or less, even morepreferably 5.4 μm or less, still preferably 5.3 μm or less, and stillmore preferably 5.2 μm or less. In addition, from a viewpoint of ease ofhandling, the thickness of the magnetic tape is preferably 3.0 μm ormore and more preferably 3.5 μm or more.

The tape thickness of the magnetic tape can be measured by the followingmethod.

Ten tape samples (for example, length of 5 to 10 cm) are cut out from arandom portion of the magnetic tape, these tape samples are overlapped,and the thickness is measured. A value which is one tenth of themeasured thickness (thickness per one tape sample) is set as the tapethickness. The thickness measurement can be performed using a well-knownmeasurement device capable of performing the thickness measurement at0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 nm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 nm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least single layer, the magnetic layer maybe separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 nm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and more preferably 0.1 to 0.7 nm.

Various thicknesses such as the thickness of the magnetic layer and thelike can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the cross section observation of theexposed cross section is performed using a scanning electron microscopeor a transmission electron microscope. Various thicknesses can beobtained as the arithmetic mean of the thicknesses obtained at tworandom portions in the cross section observation. Alternatively, variousthicknesses can be obtained as a designed thickness calculated under themanufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Composition for forming the magnetic layer, the non-magnetic layer, orthe back coating layer generally includes a solvent, together with thevarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among them, from a viewpoint of thesolubility of the binding agent usually used for the coating typemagnetic recording medium, each layer forming composition preferablycontains one or more of a ketone solvent such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of solvent in each layerforming composition is not particularly limited, and can be identical tothat in each layer forming composition of a typical coating typemagnetic recording medium. In addition, a step of preparing each layerforming composition can generally include at least a kneading step, adispersing step, and a mixing step provided before and after thesesteps, as necessary. Each step may be divided into two or more stages.The component used in the preparation of each layer forming compositionmay be added at an initial stage or in a middle stage of each step. Eachcomponent may be separately added in two or more steps. For example, abinding agent may be separately added in a kneading step, a dispersingstep, and a mixing step for adjusting viscosity after the dispersion. Inaddition, as described above, one or more kinds of nitrogen-containingpolymers and one or more kinds of the fatty acids described above areused as components of the magnetic layer forming composition, and thesalt forming reaction can proceed by mixing these in the step ofpreparing the magnetic layer forming composition. In one embodiment, oneor more kinds of nitrogen-containing polymers and one or more kinds ofthe fatty acids described above are mixed to form a salt beforepreparing the magnetic layer forming composition, and then, the magneticlayer forming composition can be prepared using this salt as a componentof the magnetic layer forming composition. This point also applies to astep of preparing the non-magnetic layer forming composition. In oneaspect, in the step of preparing the magnetic layer forming composition,a dispersion liquid including a projection formation agent (hereinafter,referred to as a “projection formation agent liquid”) can be prepared,and then this projection formation agent liquid can be mixed with one ormore other components of the magnetic layer forming composition. Forexample, the projection formation agent liquid can be prepared by awell-known dispersion process such as ultrasonic treatment. Theultrasonic treatment can be performed, for example, for about 1 to 300minutes at an ultrasonic output of about 10 to 2,000 watts per 200 cc (1cc=1 cm³). In addition, the filtering may be performed after adispersion process. For the filter used for the filtering, the followingdescription can be referred to.

In the manufacturing step of the magnetic tape, a well-knownmanufacturing technology of the related art can be used as a part ofstep or the entire step. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder is preferably used. For details ofthe kneading processes, descriptions disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A) can be referred to.In addition, glass beads and/or other beads can be used to disperse eachlayer forming composition. As such dispersion beads, zirconia beads,titania beads, and steel beads which are dispersion beads having highspecific gravity are suitable. These dispersion beads is preferably usedby optimizing a particle diameter (bead diameter) and a fillingpercentage of these dispersion beads. As a disperser, a well-knowndispersion device can be used. Each layer forming composition may befiltered by a well-known method before performing the coating step. Thefiltering can be performed by using a filter, for example. As the filterused in the filtering, a filter having a hole diameter of 0.01 to 3 μm(for example, filter made of glass fiber or filter made ofpolypropylene) can be used, for example.

Coating Step

The magnetic layer can be formed, for example, by directly applying themagnetic layer forming composition onto the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. In an case of performing an alignment process, while the coatinglayer of the magnetic layer forming composition is wet, the alignmentprocess is performed with respect to the coating layer in an alignmentzone. For the alignment process, various technologies disclosed in aparagraph 0052 of JP2010-24113A can be applied. For example, ahomeotropic alignment process can be performed by a well-known methodsuch as a method using a different polar facing magnet. The magneticfield strength in a homeotropic alignment process can be, for example,0.40 T (Tesla) to 1.20 T. The higher the magnetic field strength, thesmaller the value of vertical SFD tends to be. In the alignment zone, adrying speed of the coating layer can be controlled by a temperature andan air flow of the dry air and/or a transporting rate in the alignmentzone. In addition, the coating layer may be preliminarily dried beforetransporting to the alignment zone.

The back coating layer can be formed by applying a back coating layerforming composition onto a side of the non-magnetic support opposite tothe side provided with the magnetic layer (or to be provided with themagnetic layer). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

After performing the coating step described above, a calendar process isusually performed in order to improve surface smoothness of the magnetictape. For calendar conditions, a calendar pressure is, for example, 200to 500 kN/m and preferably 250 to 350 kN/m, a calendar temperature(surface temperature of calendar roll) is, for example, 70° C. to 120°C. and preferably 80° C. to 100° C., and a calendar speed is, forexample, 50 to 300 m/min and preferably 80 to 200 m/min. In addition, asa roll having a hard surface is used as a calendar roll, or as thenumber of stages is increased, the surface of the magnetic layer tendsto be smoother.

For various other steps for manufacturing a magnetic tape, a descriptiondisclosed in paragraphs 0067 to 0070 of JP2010-231843A can be referredto.

Through various steps, a long magnetic tape raw material can beobtained. The obtained magnetic tape raw material is, for example, cut(slit) by a well-known cutter to have a width of a magnetic tape to beaccommodated in the magnetic tape cartridge. The width can be determinedaccording to the standard and is normally 1/2 inches.

In the magnetic tape obtained by slitting, normally, a servo pattern canbe formed.

Heat Treatment

In one embodiment, the magnetic tape can be a magnetic tape manufacturedthrough the following heat treatment. In another aspect, the magnetictape can be manufactured without the following heat treatment.

The heat treatment can be performed in a state where the magnetic tapeslit and cut to have a width determined according to the standard iswound around a core member.

In one embodiment, the heat treatment is performed in a state where themagnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “core for heat treatment”), the magnetictape after the heat treatment is wound around a cartridge reel of themagnetic tape cartridge, and a magnetic tape cartridge in which themagnetic tape is wound around the cartridge reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper.The material of the core for heat treatment is preferably a materialhaving high stiffness, from a viewpoint of preventing the occurrence ofa winding defect such as spoking or the like. From this viewpoint, thecore for heat treatment is preferably formed of metal or a resin. Inaddition, as an index for stiffness, a bending elastic modulus of thematerial for the core for heat treatment is preferably equal to orgreater than 0.2 GPa (gigapascal) and more preferably equal to orgreater than 0.3 GPa. Meanwhile, since the material having highstiffness is normally expensive, the use of the core for heat treatmentof the material having stiffness exceeding the stiffness capable ofpreventing the occurrence of the winding defect causes the costincrease. By considering the viewpoint described above, the bendingelastic modulus of the material for the core for heat treatment ispreferably equal to or smaller than 250 GPa. The bending elastic modulusis a value measured based on international organization forstandardization (ISO) 178 and the bending elastic modulus of variousmaterials is well known. In addition, the core for heat treatment can bea solid or hollow core member. In a case of a hollow shape, a wallthickness is preferably equal to or greater than 2 mm, from a viewpointof maintaining the stiffness. In addition, the core for heat treatmentmay include or may not include a flange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length”) is prepared as the magnetictape wound around the core for heat treatment, and it is preferable toperform the heat treatment by placing the magnetic tape in the heattreatment environment, in a state where the magnetic tape is woundaround the core for heat treatment. The magnetic tape length woundaround the core for heat treatment is equal to or greater than the finalproduct length, and is preferably the “final product length+α”, from aviewpoint of ease of winding around the core for heat treatment. This ais preferably equal to or greater than 5 m, from a viewpoint of ease ofthe winding. The tension in a case of winding around the core for heattreatment is preferably equal to or greater than 0.1 N (newton). Inaddition, from a viewpoint of preventing the occurrence of excessivedeformation during the manufacturing, the tension in a case of windingaround the core for heat treatment is preferably equal to or smallerthan 1.5 N and more preferably equal to or smaller than 1.0 N. An outerdiameter of the core for heat treatment is preferably equal to orgreater than 20 mm and more preferably equal to or greater than 40 mm,from viewpoints of ease of the winding and preventing coiling (curl inlongitudinal direction). The outer diameter of the core for heattreatment is preferably equal to or smaller than 100 mm and morepreferably equal to or smaller than 90 mm. A width of the core for heattreatment may be equal to or greater than the width of the magnetic tapewound around this core. In addition, after the heat treatment, in a caseof detaching the magnetic tape from the core for heat treatment, it ispreferable that the magnetic tape and the core for heat treatment aresufficiently cooled and magnetic tape is detached from the core for heattreatment, in order to prevent the occurrence of the tape deformationwhich is not intended during the detaching operation. It is preferablethe detached magnetic tape is wound around another core temporarily(referred to as a “core for temporary winding”), and the magnetic tapeis wound around a cartridge reel (generally, outer diameter isapproximately 40 to 50 mm) of the magnetic tape cartridge from the corefor temporary winding. Accordingly, a relationship between the insideand the outside with respect to the core for heat treatment of themagnetic tape in a case of the heat treatment can be maintained and themagnetic tape can be wound around the cartridge reel of the magnetictape cartridge. Regarding the details of the core for temporary windingand the tension in a case of winding the magnetic tape around the core,the description described above regarding the core for heat treatmentcan be referred to. In an aspect in which the heat treatment issubjected to the magnetic tape having a length of the “final productlength+α”, the length corresponding to “+α” may be cut in any stage. Forexample, in one aspect, the magnetic tape having the final productlength may be wound around the reel of the magnetic tape cartridge fromthe core for temporary winding and the remaining length correspondingthe “+α” may be cut. From a viewpoint of decreasing the amount of theportion to be cut out and removed, the a is preferably equal to orsmaller than 20 m.

The specific aspect of the heat treatment performed in a state of beingwound around the core member as described above is described below.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as a “heat treatment temperature”) ispreferably equal to or higher than 40° C. and more preferably equal toor higher than 50° C. On the other hand, from a viewpoint of preventingthe excessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C. and more preferably equal to or lower than70° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability by dew condensation. The heattreatment time is preferably equal to or longer than 0.3 hours and morepreferably equal to or longer than 0.5 hours. In addition, the heattreatment time is preferably equal to or shorter than 48 hours, from aviewpoint of production efficiency.

Regarding the control of the standard deviation of the curvaturedescribed above, as any value of the heat treatment temperature, heattreatment time, modulus of bending elasticity of a core for the heattreatment, and tension at the time of winding around the core for theheat treatment is large, the value of the curvature tends to furtherdecrease.

Formation of Servo Pattern

The “formation of the servo pattern” can be “recording of a servosignal”. The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction ofthe magnetic tape. As a system of control using a servo signal (servocontrol), timing-based servo (TBS), amplitude servo, or frequency servois used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June2001), a timing-based servo system is used in a magnetic tape based on alinear tape-open (LTO) standard (generally referred to as an “LTOtape”). In this timing-based servo system, the servo pattern isconfigured by continuously disposing a plurality of pairs of magneticstripes (also referred to as “servo stripes”) not parallel to each otherin a longitudinal direction of the magnetic tape. In the invention andthe specification, the “timing-based servo pattern” refers to a servopattern that enables head tracking in a servo system of a timing-basedservo system. As described above, a reason for that the servo pattern isconfigured with one pair of magnetic stripes not parallel to each otheris because a servo signal reading element passing on the servo patternrecognizes a passage position thereof. Specifically, one pair of themagnetic stripes are formed so that a gap thereof is continuouslychanged along the width direction of the magnetic tape, and a relativeposition of the servo pattern and the servo signal reading element canbe recognized, by the reading of the gap thereof by the servo signalreading element. The information of this relative position can realizethe tracking of a data track. Accordingly, a plurality of servo tracksare generally set on the servo pattern along the width direction of themagnetic tape.

The servo band is configured of servo patterns continuous in thelongitudinal direction of the magnetic tape. A plurality of servo bandsare normally provided on the magnetic tape. For example, the numberthereof is 5 in the LTO tape. A region interposed between two adjacentservo bands is a data band. The data band is configured of a pluralityof data tracks and each data track corresponds to each servo track.

In one aspect, as shown in JP2004-318983A, information showing thenumber of servo band (also referred to as “servo band identification(ID)” or “Unique Data Band Identification Method (UDIM) information”) isembedded in each servo band. This servo band ID is recorded by shiftinga specific servo stripe among the plurality of pair of servo stripes inthe servo band so that the position thereof is relatively deviated inthe longitudinal direction of the magnetic tape. Specifically, theposition of the shifted specific servo stripe among the plurality ofpair of servo stripes is changed for each servo band. Accordingly, therecorded servo band ID becomes unique for each servo band, andtherefore, the servo band can be uniquely specified by only reading oneservo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method asshown in ECMA-319 (June 2001) is used. In this staggered method, aplurality of the groups of one pair of magnetic stripes (servo stripe)not parallel to each other which are continuously disposed in thelongitudinal direction of the magnetic tape is recorded so as to beshifted in the longitudinal direction of the magnetic tape for eachservo band. A combination of this shifted servo band between theadjacent servo bands is set to be unique in the entire magnetic tape,and accordingly, the servo band can also be uniquely specified byreading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing theposition in the longitudinal direction of the magnetic tape (alsoreferred to as “Longitudinal Position (LPOS) information”) is normallyembedded in each servo band. This LPOS information is recorded so thatthe position of one pair of servo stripes is shifted in the longitudinaldirection of the magnetic tape, in the same manner as the UDIMinformation. However, unlike the UDIM information, the same signal isrecorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOSinformation can be embedded in the servo band. In this case, theembedded information may be different for each servo band as the UDIMinformation, or may be common in all of the servo bands, as the LPOSinformation.

In addition, as a method of embedding the information in the servo band,a method other than the method described above can be used. For example,a predetermined code may be recorded by thinning out a predeterminedpair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head.The servo write head generally includes pairs of gaps corresponding tothe pairs of magnetic stripes by the number of servo bands. In general,a core and a coil are respectively connected to each of the pairs ofgaps, and a magnetic field generated in the core can generate leakagemagnetic field in the pairs of gaps, by supplying a current pulse to thecoil. In a case of forming the servo pattern, by inputting a currentpulse while causing the magnetic tape to run on the servo write head,the magnetic pattern corresponding to the pair of gaps is transferred tothe magnetic tape, and the servo pattern can be formed. A width of eachgap can be suitably set in accordance with a density of the servopattern to be formed. The width of each gap can be set as, for example,equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization(erasing) process is generally performed on the magnetic tape. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape by using a DC magnet and an AC magnet. The erasingprocess includes direct current (DC) erasing and alternating current(AC) erasing. The AC erasing is performed by slowing decreasing anintensity of the magnetic field, while reversing a direction of themagnetic field applied to the magnetic tape. Meanwhile, the DC erasingis performed by applying the magnetic field in one direction to themagnetic tape. The DC erasing further includes two methods. A firstmethod is horizontal DC erasing of applying the magnetic field in onedirection along a longitudinal direction of the magnetic tape. A secondmethod is vertical DC erasing of applying the magnetic field in onedirection along a thickness direction of the magnetic tape. The erasingprocess may be performed with respect to all of the magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed isdetermined in accordance with the direction of erasing. For example, ina case where the horizontal DC erasing is performed to the magnetictape, the formation of the servo pattern is performed so that thedirection of the magnetic field and the direction of erasing is oppositeto each other. Accordingly, the output of the servo signal obtained bythe reading of the servo pattern can be increased. As disclosed inJP2012-53940A, in a case where the magnetic pattern is transferred tothe magnetic tape subjected to the vertical DC erasing by using the gap,the servo signal obtained by the reading of the formed servo pattern hasa unipolar pulse shape. Meanwhile, in a case where the magnetic patternis transferred to the magnetic tape subjected to the horizontal DCerasing by using the gap, the servo signal obtained by the reading ofthe formed servo pattern has a bipolar pulse shape.

Magnetic Tape Cartridge

According to another aspect of the present invention, there is provideda magnetic tape cartridge including the magnetic tape described above.

The details of the magnetic tape included in the magnetic tape cartridgeare as described above.

In the magnetic tape cartridge, the magnetic tape is generallyaccommodated in a cartridge main body in a state of being wound around areel. The reel is rotatably provided in the cartridge main body. As themagnetic tape cartridge, a single reel type magnetic tape cartridgeincluding one reel in a cartridge main body and a twin reel typemagnetic tape cartridge including two reels in a cartridge main body arewidely used. In a case where the single reel type magnetic tapecartridge is mounted in the magnetic tape device in order to recordand/or reproduce data on the magnetic tape, the magnetic tape is drawnfrom the magnetic tape cartridge and wound around the reel on themagnetic tape device side. A magnetic head is disposed on a magnetictape transportation path from the magnetic tape cartridge to a windingreel. Feeding and winding of the magnetic tape are performed between areel (supply reel) on the magnetic tape cartridge side and a reel(winding reel) on the magnetic tape device side. In the meantime, themagnetic head comes into contact with and slides on the surface of themagnetic layer of the magnetic tape, and accordingly, the recordingand/or reproducing of data is performed. With respect to this, in thetwin reel type magnetic tape cartridge, both reels of the supply reeland the winding reel are provided in the magnetic tape cartridge.

In one aspect, the magnetic tape cartridge can include a cartridgememory. The cartridge memory can be, for example, a non-volatile memory,and head tilt angle adjustment information is recorded in advance orhead tilt angle adjustment information is recorded. The head tilt angleadjustment information is information for adjusting the head tilt angleduring the running of the magnetic tape in the magnetic tape device. Forexample, as the head tilt angle adjustment information, a value of theservo band spacing at each position in the longitudinal direction of themagnetic tape at the time of data recording can be recorded. Forexample, in a case where the data recorded on the magnetic tape isreproduced, the value of the servo band spacing is measured at the timeof the reproducing, and the head tilt angle can be changed by thecontrol device of the magnetic tape device so that an absolute value ofa difference of the servo band spacing at the time of recording at thesame longitudinal position recorded in the cartridge memory is close to0. The head tilt angle can be, for example, the angle θ described above.

The magnetic tape and the magnetic tape cartridge can be suitably usedin the magnetic tape device (that is, magnetic recording and reproducingsystem) for performing recording and/or reproducing data at differenthead tilt angles. In such a magnetic tape device, in one embodiment, itis possible to perform the recording and/or reproducing of data bychanging the head tilt angle during running of a magnetic tape. Forexample, the head tilt angle can be changed according to dimensionalinformation of the magnetic tape in the width direction obtained whilethe magnetic tape is running. In addition, for example, in a usageaspect, a head tilt angle during the recording and/or reproducing at acertain time and a head tilt angle during the recording and/orreproducing at the next time and subsequent times are changed, and thenthe head tilt angle may be fixed without changing during the running ofthe magnetic tape for the recording and/or reproducing of each time. Inany usage aspect, a magnetic tape having high running stability in acase of performing the recording and/or reproducing of data at differenthead tilt angles is preferable.

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape device includingthe magnetic tape described above. In the magnetic tape device, therecording of data on the magnetic tape and/or the reproducing of datarecorded on the magnetic tape can be performed by bringing the surfaceof the magnetic layer of the magnetic tape into contact with themagnetic head and sliding. The magnetic tape device can attachably anddetachably include the magnetic tape cartridge according to oneembodiment of the invention.

The magnetic tape cartridge can be attached to a magnetic tape deviceprovided with a magnetic head and used for performing the recordingand/or reproducing of data. In the invention and the specification, the“magnetic tape device” means a device capable of performing at least oneof the recording of data on the magnetic tape or the reproducing of datarecorded on the magnetic tape. Such a device is generally called adrive.

Magnetic Head

The magnetic tape device can include a magnetic head. The configurationof the magnetic head and the angle θ, which is the head tilt angle, areas described above with reference to FIGS. 1 to 3 . The magnetic headincluded in the magnetic tape device can be an LTO8 head in one aspect,an LTO head of another generation in another aspect, and a magnetic headother than the LTO head in still another aspect. In a case where themagnetic head includes a reproducing element, as the reproducingelement, a magnetoresistive (MR) element capable of reading informationrecorded on the magnetic tape with excellent sensitivity is preferable.As the MR element, various well-known MR elements (for example, a GiantMagnetoresistive (GMR) element, or a Tunnel Magnetoresistive (TMR)element) can be used. Hereinafter, the magnetic head which records dataand/or reproduces the recorded data is also referred to as a “recordingand reproducing head”. The element for recording data (recordingelement) and the element for reproducing data (reproducing element) arecollectively referred to as a “magnetic head element”.

By reproducing data using the reproducing element having a narrowreproducing element width as the reproducing element, the data recordedat high density can be reproduced with high sensitivity. From thisviewpoint, the reproducing element width of the reproducing element ispreferably 0.8 μm or less. The reproducing element width of thereproducing element can be, for example, 0.3 μm or more. However, it isalso preferable to fall below this value from the above viewpoint.

Here, the “reproducing element width” refers to a physical dimension ofthe reproducing element width. Such physical dimensions can be measuredwith an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first,tracking using a servo signal can be performed. That is, as the servosignal reading element follows a predetermined servo track, the magnetichead element can be controlled to pass on the target data track. Themovement of the data track is performed by changing the servo track tobe read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform therecording and/or reproducing with respect to other data bands. In thiscase, the servo signal reading element is moved to a predetermined servoband by using the UDIM information described above, and the trackingwith respect to the servo band may be started.

FIG. 5 shows an example of disposition of data bands and servo bands. InFIG. 5 , a plurality of servo bands 1 are disposed to be interposedbetween guide bands 3 in a magnetic layer of a magnetic tape MT. Aplurality of regions 2 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 6 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 6 , a servo frameSF on the servo band 1 is configured with a servo sub-frame 1 (SSF1) anda servo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with anA burst (in FIG. 6 , reference numeral A) and a B burst (in FIG. 6 ,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG. 6, reference numeral C) and a D burst (in FIG. 6 , reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for recognizingthe servo frames. FIG. 6 shows one servo frame for explaining. However,in practice, in the magnetic layer of the magnetic tape in which thehead tracking servo in the timing-based servo system is performed, aplurality of servo frames are disposed in each servo band in a runningdirection. In FIG. 6 , an arrow shows a magnetic tape running direction.For example, an LTO Ultrium format tape generally includes 5,000 or moreservo frames per a tape length of 1 m, in each servo band of themagnetic layer.

In the magnetic tape device, the head tilt angle can be changed whilethe magnetic tape is running in the magnetic tape device. The head tiltangle is, for example, an angle θ formed by the axis of the elementarray with respect to the width direction of the magnetic tape. Theangle θ is as described above. For example, by providing an angleadjustment unit for adjusting the angle of the module of the magnetichead in the recording and reproducing head unit of the magnetic head,the angle θ can be variably adjusted during the running of the magnetictape. Such an angle adjustment unit can include, for example, a rotationmechanism for rotating the module. For the angle adjustment unit, awell-known technology can be applied.

Regarding the head tilt angle during the running of the magnetic tape,in a case where the magnetic head includes a plurality of modules, theangle θ described with reference to FIGS. 1 to 3 can be specified forthe randomly selected module. The angle θ at the start of running of themagnetic tape, θ_(initial), can be set to 0° or more or more than 0°. Asthe θ_(initial) is large, change amount of the distance between theservo signal reading elements with respect to a change amount of theangle θ increases, and accordingly, it is preferable from a viewpoint ofadjustment ability for adjusting the distance between the servo signalreading elements according to the dimension change of the widthdirection of the magnetic tape. From this viewpoint, the θ_(initial) ispreferably 1° or more, more preferably 5° or more, and even morepreferably 10° or more. Meanwhile, regarding an angle (generallyreferred to as a “lap angle”) formed by a surface of the magnetic layerand a contact surface of the magnetic head in a case where the magnetictape runs and comes into contact with the magnetic head, a deviation ina tape width direction which is kept small is effective in improvinguniformity of friction in the tape width direction which is generated bythe contact between the magnetic head and the magnetic tape during therunning of the magnetic tape. In addition, it is desirable to improvethe uniformity of the friction in the tape width direction from aviewpoint of position followability and the running stability of themagnetic head. From a viewpoint of reducing the deviation of the lapangle in the tape width direction, θ_(initial) is preferably 45° orless, more preferably 40° or less, and even more preferably 35° or less.

Regarding the change of the angle θ during the running of the magnetictape, while the magnetic tape is running in the magnetic tape device inorder to record data on the magnetic tape and/or to reproduce datarecorded on the magnetic tape, in a case where the angle θ of themagnetic head changes from θ_(initial) at the start of running, amaximum change amount Δθ of the angle θ during the running of themagnetic tape is a larger value among Δθ_(max) and Δθ_(min) calculatedby the following equation. A maximum value of the angle θ during therunning of the magnetic tape is θ_(max), and a minimum value thereof isθ_(min). In addition, “max” is an abbreviation for maximum, and “min” isan abbreviation for minimum.Δθ_(max)=θ_(max)−θ_(initial) andΔθ_(min)=θ_(initial)−θ_(min.)

In one embodiment, the Δθ can be more than 0.000°, and is preferably0.001° or more and more preferably 0.010° or more, from a viewpoint ofadjustment ability for adjusting the effective distance between theservo signal reading elements according to the dimension change in thewidth direction of the magnetic tape. In addition, from a viewpoint ofease of ensuring synchronization of recorded data and/or reproduced databetween a plurality of magnetic head elements during data recordingand/or reproducing, the Δθ is preferably 1.000° or less, more preferably0.900° or less, even more preferably 0.800° or less, still preferably0.700° or less, and still more preferably 0.600° or less.

In the examples shown in FIGS. 2 and 3 , the axis of the element arrayis tilted toward a magnetic tape running direction. However, the presentinvention is not limited to such an example. The present invention alsoincludes an aspect in which the axis of the element array is tilted in adirection opposite to the magnetic tape running direction in themagnetic tape device.

The head tilt angle θ_(initial) at the start of the running of themagnetic tape can be set by a control device or the like of the magnetictape device.

Regarding the head tilt angle during the running of the magnetic tape,FIG. 7 is an explanatory diagram of a method for measuring the angle θduring the running of the magnetic tape. The angle θ during the runningof the magnetic tape can be obtained, for example, by the followingmethod. In a case where the angle θ during traveling on the magnetictape is obtained by the following method, the angle θ is changed in arange of 0° to 90° during the running of the magnetic tape. That is, ina case where the axis of the element array is tilted toward the magnetictape running direction at the start of running of the magnetic tape, theelement array is not tilted so that the axis of the element array tiltstoward a direction opposite to the magnetic tape running direction atthe start of the running of the magnetic tape, during the running of themagnetic tape, and in a case where the axis of the element array istilted toward the direction opposite to the magnetic tape runningdirection at the start of running of the magnetic tape, the elementarray is not tilted so that the axis of the element array tilts towardthe magnetic tape running direction at the start of the running of themagnetic tape, during the running of the magnetic tape.

A phase difference (that is, time difference) AT of reproduction signalsof the pair of servo signal reading elements 1 and 2 is measured. Themeasurement of AT can be performed by a measurement unit provided in themagnetic tape device. A configuration of such a measurement unit is wellknown. A distance L between a central portion of the servo signalreading element 1 and a central portion of the servo signal readingelement 2 can be measured with an optical microscope or the like. In acase where a running speed of the magnetic tape is defined as a speed v,the distance in the magnetic tape running direction between the centralportions of the two servo signal reading elements is set to Lsinθ, and arelationship of Lsinθ=v×ΔT is satisfied. Therefore, the angle θ duringthe running of the magnetic tape can be calculated by a formula“θ=arcsin (vΔT/L)”. The right drawing of FIG. 7 shows an example inwhich the axis of the element array is tilted toward the magnetic taperunning direction. In this example, the phase difference (that is, timedifference) ΔT of a phase of the reproduction signal of the servo signalreading element 2 with respect to a phase of the reproduction signal ofthe servo signal reading element 1 is measured. In a case where the axisof the element array is tilted toward the direction opposite to therunning direction of the magnetic tape, θ can be obtained by the methoddescribed above, except for measuring ΔT as the phase difference (thatis, time difference) of the phase of the reproduction signal of theservo signal reading element 1 with respect to the phase of thereproduction signal of the servo signal reading element 2.

For a measurement pitch of the angle θ, that is, a measurement intervalof the angle θ in a tape longitudinal direction, a suitable pitch can beselected according to a frequency of tape width deformation in the tapelongitudinal direction. As an example, the measurement pitch can be, forexample, 250 μm.

Configuration of Magnetic Tape Device

A magnetic tape device 10 shown in FIG. 8 controls a recording andreproducing head unit 12 in accordance with a command from a controldevice 11 to record and reproduce data on a magnetic tape MT.

The magnetic tape device 10 has a configuration of detecting andadjusting a tension applied in a longitudinal direction of the magnetictape from spindle motors 17A and 17B and driving devices 18A and 18Bwhich rotatably control a magnetic tape cartridge reel and a windingreel.

The magnetic tape device 10 has a configuration in which the magnetictape cartridge 13 can be mounted.

The magnetic tape device 10 includes a cartridge memory read and writedevice 14 capable of performing reading and writing with respect to thecartridge memory 131 in the magnetic tape cartridge 13.

An end portion or a leader pin of the magnetic tape MT is pulled outfrom the magnetic tape cartridge 13 mounted on the magnetic tape device10 by an automatic loading mechanism or manually and passes on arecording and reproducing head through guide rollers 15A and 15B so thata surface of a magnetic layer of the magnetic tape MT comes into contactwith a surface of the recording and reproducing head of the recordingand reproducing head unit 12, and accordingly, the magnetic tape MT iswound around the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor17B are controlled by a signal from the control device 11, and themagnetic tape MT runs at random speed and tension. A servo patternpreviously formed on the magnetic tape can be used to control the tapespeed and control the head tilt angle. A tension detection mechanism maybe provided between the magnetic tape cartridge 13 and the winding reel16 to detect the tension. The tension may be controlled by using theguide rollers 15A and 15B in addition to the control by the spindlemotors 17A and 17B.

The cartridge memory read and write device 14 is configured to be ableto read and write information of the cartridge memory 131 according tocommands from the control device 11. As a communication system betweenthe cartridge memory read and write device 14 and the cartridge memory131, for example, an international organization for standardization(ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storageunit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example,a recording and reproducing head, a servo tracking actuator foradjusting a position of the recording and reproducing head in a trackwidth direction, a recording and reproducing amplifier 19, a connectorcable for connecting to the control device 11. The recording andreproducing head is composed of, for example, a recording element forrecording data on a magnetic tape, a reproducing element for reproducingdata of the magnetic tape, and a servo signal reading element forreading a servo signal recorded on the magnetic tape. For example, oneor more of each of the recording elements, the reproducing element, andthe servo signal reading element are mounted in one magnetic head.Alternatively, each element may be separately provided in a plurality ofmagnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able torecord data on the magnetic tape MT according to a command from thecontrol device 11. In addition, the data recorded on the magnetic tapeMT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo trackingactuator so as to obtain a running position of the magnetic tape from aservo signal read from a servo band during the running of the magnetictape MT and position the recording element and/or the reproducingelement at a target running position (track position). The control ofthe track position is performed by feedback control, for example. Thecontrol device 11 has a mechanism of obtaining a servo band spacing fromservo signals read from two adjacent servo bands during the running ofthe magnetic tape MT. The control device 11 can store the obtainedinformation of the servo band spacing in the storage unit inside thecontrol device 11, the cartridge memory 131, an external connectiondevice, and the like. In addition, the control device 11 can change thehead tilt angle according to the dimensional information in the widthdirection of the magnetic tape during the running Accordingly, it ispossible to bring the effective distance between the servo signalreading elements closer to or match the spacing of the servo bands. Thedimensional information can be obtained by using the servo patternpreviously formed on the magnetic tape. For example, by doing so, theangle θ formed by the axis of the element array with respect to thewidth direction of the magnetic tape can be changed during the runningof the magnetic tape in the magnetic tape device according todimensional information of the magnetic tape in the width directionobtained during the running The head tilt angle can be adjusted, forexample, by feedback control. Alternatively, for example, the head tiltangle can also be adjusted by a method disclosed in JP2016-524774A orUS2019/0164573A1.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to the embodiments shown in theexamples. “Parts” in the following description indicates “parts bymass”. In addition, steps and evaluations described below are performedin an environment of an atmosphere temperature of 23° C.±1° C., unlessotherwise noted. “eq” described below indicates equivalent and a unitnot convertible into SI unit.

Projection Formation Agent

A projection formation agent used in the preparation of the magneticlayer forming composition for manufacturing the magnetic tape ofexamples or comparative examples is as follows. A projection formationagent A and a projection formation agent D are particles having a lowsurface smoothness of a surface of particles. A particle shape of aprojection formation agent B is a so-called unspecified shape. Aparticle shape of a projection formation agent C is a shape of a cocoon.A particle shape of a projection formation agent E is a shape closer toa sphere.

Projection formation agent A: ATLAS (composite particles of silica andpolymer) manufactured by Cabot Corporation, average particle size: 100nm

Projection formation agent B: ASAHI #52 (carbon black) manufactured byAsahi Carbon Co., Ltd., average particle size: 60 nm

Projection formation agent C: TGC6020N (silica particles) manufacturedby Cabot Corporation, average particle size: 140 nm

Projection formation agent D: Cataloid (water dispersed sol of silicaparticles; as a projection formation agent for preparing a magneticlayer forming composition, a dried solid material obtained by removingthe solvent by heating the water dispersed sol described above is used)manufactured by JGC c&c, average particle size: 120 nm

Projection formation agent E: PL-10L (water dispersed sol of silicaparticles; as a projection formation agent for preparing a magneticlayer forming composition, a dried solid material obtained by removingthe solvent by heating the water dispersed sol described above is used)manufactured by FUSO CHEMICAL CO., LTD., average particle size: 130 nm

Ferromagnetic Powder

In Table 1, “BaFe” is a hexagonal barium ferrite powder (coercivity Hc:196 kA/m, an average particle size (average plate diameter): 24 nm).

In Table 1, “SrFe1” is a hexagonal strontium ferrite powder produced bythe following method.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed ina mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,390° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace,heated to 635° C. (crystallization temperature) at a rate of temperaturerise of 3.5° C./min, and held at the same temperature for 5 hours, andhexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1000 g of zirconia beads having a particle diameter of 1 mm and800 ml of an acetic acid aqueous solution having a concentration of 1%were added to a glass bottle, and a dispersion process was performed ina paint shaker for 3 hours. After that, the obtained dispersion liquidand the beads were separated and put in a stainless still beaker. Thedispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 18 nm, an activation volume was 902nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a massmagnetization σs was 49 A×m²/kg.

12 mg of a sample powder was collected from the hexagonal strontiumferrite powder obtained as described above, the element analysis of afiltrate obtained by the partial dissolving of this sample powder underthe dissolving conditions described above was performed by the ICPanalysis device, and a surface layer portion content of a neodymium atomwas obtained.

Separately, 12 mg of a sample powder was collected from the hexagonalstrontium ferrite powder obtained as described above, the elementanalysis of a filtrate obtained by the total dissolving of this samplepowder under the dissolving conditions described above was performed bythe ICP analysis device, and a bulk content of a neodymium atom wasobtained.

The content (bulk content) of the neodymium atom in the hexagonalstrontium ferrite powder obtained as described above with respect to 100atom % of iron atom was 2.9 atom %. In addition, the surface layerportion content of the neodymium atom was 8.0 atom %. A ratio of thesurface layer portion content and the bulk content, “surface layerportion content/bulk content” was 2.8 and it was confirmed that theneodymium atom is unevenly distributed on the surface layer of theparticles.

A crystal structure of the hexagonal ferrite shown by the powderobtained as described above was confirmed by scanning CuKα ray under theconditions of a voltage of 45 kV and intensity of 40 mA and measuring anX-ray diffraction pattern under the following conditions (X-raydiffraction analysis). The powder obtained as described above showed acrystal structure of magnetoplumbite type (M type) hexagonal ferrite. Inaddition, a crystal phase detected by the X-ray diffraction analysis wasa magnetoplumbite type single phase.

PANalytical X′Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: 1/4 degrees

Mask: 10 mm

Scattering prevention slit: 1/4 degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” is a hexagonal strontium ferrite powder produced bythe following method.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer toobtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,380° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace,heated to 645° C. (crystallization temperature), and held at the sametemperature for 5 hours, and hexagonal strontium ferrite particles wereprecipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1000 g of zirconia beads having a particle diameter of 1 mm and800 ml of an acetic acid aqueous solution having a concentration of 1%were added to a glass bottle, and a dispersion process was performed ina paint shaker for 3 hours. After that, the obtained dispersion liquidand the beads were separated and put in a stainless still beaker. Thedispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 19 nm, an activation volume was1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a massmagnetization σs was 50 A×m²/kg.

In Table 1, “ε-iron oxide” is an ε-iron oxide powder produced by thefollowing method.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 8.3 g of iron (III) nitratenonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg ofcobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, whilestirring by using a magnetic stirrer, in an atmosphere under theconditions of an atmosphere temperature of 25° C., and the mixture wasstirred for 2 hours still under the temperature condition of theatmosphere temperature of 25° C. A citric acid aqueous solution obtainedby dissolving 1 g of citric acid in 9 g of pure water was added to theobtained solution and stirred for 1 hour. The powder precipitated afterthe stirring was collected by centrifugal separation, washed with purewater, and dried in a heating furnace at a furnace inner temperature of80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodiumhydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, theliquid temperature was held at 70° C., stirring was performed for 24hours, and accordingly, a silicon acid compound which was an impuritywas removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the X-ray diffraction analysis was performed under the same conditionsas disclosed regarding SrFe1 above, and it was confirmed that theobtained ferromagnetic powder has a crystal structure of a single phasewhich is an ε phase not including a crystal structure of an α phase anda γ phase (ε-iron oxide type crystal structure) from the peak of theX-ray diffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle sizewas 12 nm, an activation volume was 746 nm³, an anisotropy constant Kuwas 1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonalstrontium ferrite powder and the ε-iron oxide powder are values obtainedby the method described above regarding each ferromagnetic powder byusing an oscillation sample type magnetic-flux meter (manufactured byToei Industry Co., Ltd.).

The mass magnetization σs is a value measured using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.) at a magnetic field strength of 15 kOe.

Example 1

-   -   Magnetic Layer Forming Composition    -   Magnetic Liquid    -   Ferromagnetic powder (see Table 1): 100.0 parts    -   Oleic acid: 2.0 parts    -   Vinyl chloride copolymer (MR-104 manufactured by Kaneka        Corporation): 10.0 parts    -   SO₃Na group-containing polyurethane resin: 4.0 parts    -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.07        meq/g)    -   Additive A: 10.0 parts    -   Methyl ethyl ketone: 150.0 parts    -   Cyclohexanone: 150.0 parts    -   Abrasive solution    -   α-alumina (Average particle size: 110 nm): 6.0 parts    -   Vinyl chloride copolymer (MR 110 manufactured by Kaneka        Corporation): 0.7 parts    -   Cyclohexanone: 20.0 parts    -   Projection formation agent liquid    -   Projection formation agent (see Table 1): See Table 1    -   Methyl ethyl ketone: 9.0 parts    -   Cyclohexanone: 6.0 parts    -   Other Components    -   Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.,        number average    -   molecular weight: 300): 2.0 parts    -   Stearic acid: 0.5 parts    -   Stearic acid amide: 0.3 parts    -   Butyl stearate: 6.0 parts    -   Methyl ethyl ketone: 110.0 parts    -   Cyclohexanone: 110.0 parts    -   Polyisocyanate (CORONATE (registered product) L manufactured by        Tosoh Corporation): 3.0 parts

The additive A described above is a polymer synthesized by the methoddisclosed in paragraphs 0115 to 0123 of JP2016-051493A.

-   -   Non-Magnetic Layer Forming Composition    -   Non-magnetic inorganic powder (α-iron oxide): 80.0 parts    -   (Average particle size: 0.15 μm, average acicular ratio: 7,        Brunauer-Emmett-Teller (BET) specific surface area: 52 m²/g)    -   Carbon black (average particle size: 20 nm): 20.0 parts    -   Electron beam curable vinyl chloride copolymer: 13.0 parts    -   Electron beam curable polyurethane resin: 6.0 parts    -   Phenylphosphonic acid: 3.0 parts    -   Cyclohexanone: 140.0 parts    -   Methyl ethyl ketone: 170.0 parts    -   Butyl stearate: 2.0 parts    -   Stearic acid: 1.0 part    -   Back Coating Layer Forming Composition    -   Non-magnetic inorganic powder (a-iron oxide): 80.0 parts    -   (Average particle size: 0.15 μm, average acicular ratio: 7, BET        specific surface area: 52 m²/g)    -   Carbon black (average particle size: 20 nm): 20.0 parts    -   Carbon black (average particle size: 100 nm): 3.0 parts    -   A vinyl chloride copolymer: 13.0 parts    -   Sulfonic acid group-containing polyurethane resin: 6.0 parts    -   Phenylphosphonic acid: 3.0 parts    -   Cyclohexanone: 140.0 parts    -   Methyl ethyl ketone: 170.0 parts    -   Stearic acid: 3.0 parts    -   Polyisocyanate (CORONATE (registered product) L manufactured by        Tosoh Corporation): 5.0 parts    -   Methyl ethyl ketone: 400.0 parts

Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

The components of the magnetic liquid were kneaded by an open kneaderand diluted, and was subjected to a dispersion process of 12 passes,with a transverse beads mill disperser and zirconia (ZrO₂) beads havinga particle diameter of 0.5 mm (hereinafter, referred to as “Zr beads”),by setting a bead filling percentage as 80 volume %, a circumferentialspeed of rotor distal end as 10 msec, and a retention time for 1 passfor 2 minutes.

Regarding the abrasive solution, components of the abrasive solutionwere mixed and put in a vertical sand mill disperser together with Zrbeads having a particle diameter of 1 mm, so as to perform theadjustment so that a value of bead volume/(abrasive solution volume+beadvolume) was 60%, the sand mill dispersion process was performed for 180minutes, the liquid after the process was extracted, and an ultrasonicdispersion filtering process was performed by using a flow typeultrasonic dispersion filtering device.

The projection formation agent liquid was prepared by filtering adispersion liquid obtained by mixing the components of theabove-mentioned projection formation agent liquid and thenultrasonically treating (dispersing) for 60 minutes with an ultrasonicoutput of 500 watts per 200 cc by a horn-type ultrasonic dispersingdevice with a filter having a hole size of 0.5 μm.

The magnetic liquid, the abrasive solution, the projection formationagent liquid, and the other components were introduced in a dissolverstirrer, and stirred at a circumferential speed of 10 m/sec for 30minutes. Then, a process at a flow rate of 7.5 kg/min was performed for3 passes with a flow type ultrasonic disperser, and then, the mixturewas filtered with a filter having a hole diameter of 1 μm, to prepare amagnetic layer forming composition.

The non-magnetic layer forming composition was prepared by the followingmethod.

The components excluding the lubricant (butyl stearate and stearic acid)were kneaded and diluted with an open kneader, and then dispersed with atransverse beads mill disperser. Then, the lubricant (butyl stearate andstearic acid) was added, and the mixture was stirred and mixed with adissolver stirrer to prepare a non-magnetic layer forming composition.

The back coating layer forming composition was prepared by the followingmethod.

The components excluding the lubricant (stearic acid), polyisocyanate,and methyl ethyl ketone (400.0 parts) were kneaded and diluted with anopen kneader, and then dispersed with a transverse beads mill disperser.Then, the lubricant (stearic acid), polyisocyanate, and methyl ethylketone (400.0 parts) were added, and the mixture was stirred and mixedwith a dissolver stirrer to prepare a back coating layer formingcomposition.

Manufacturing of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition was applied to a biaxialstretching support made of polyethylene naphthalate having a thicknessof 4.1 μm so that the thickness after the drying is 0.7 μm and was driedto emit an electron ray to have energy of 40 kGy at an accelerationvoltage of 125 kV. The magnetic layer forming composition was appliedthereon so that the thickness after the drying is 0.1 μm, and a coatinglayer was formed. A homeotropic alignment process was performed byapplying a magnetic field having a magnetic field strength shown inTable 1 in a vertical direction with respect to a surface of a coatinglayer, in the alignment zone, while the coating layer of the magneticlayer forming composition is wet. Then, the drying was performed to formthe magnetic layer. After that, the back coating layer formingcomposition as described above was applied to the surface of the supportopposite to the surface where the non-magnetic layer and the magneticlayer were formed, so that the thickness after the drying becomes 0.3μm, and was dried to form a back coating layer.

Then, a calender process was performed by using a 7-stage calender rollconfigured of only a metal roll, at a calendar speed of 80 m/min, linearpressure of 294 kN/m, and a calender temperature (surface temperature ofa calender roll) of 80° C. Then, the heat treatment was performed in theenvironment of the ambient temperature of 70° C. for 36 hours. Afterheat treatment, the slitting was performed so as to have a width of ½inches, and the surface of the magnetic layer was cleaned with a tapecleaning device in which a nonwoven fabric and a razor blade areattached to a device including a sending and winding devices of the slitproduct to press the surface of the magnetic layer, and the magnetictape was obtained.

By recording a servo signal on a magnetic layer of the obtained magnetictape with a commercially available servo writer, and including a servopattern (timing-based servo pattern) having the disposition and shapeaccording to the linear tape-open (LTO) Ultrium format on the servo bandwas obtained.

Accordingly, a magnetic tape including data bands, servo bands, andguide bands in the disposition according to the LTO Ultrium format inthe magnetic layer, and including servo patterns (timing-based servopattern) having the disposition and the shape according to the LTOUltrium format on the servo band was obtained. The servo pattern formedby doing so is a servo pattern disclosed in Japanese IndustrialStandards (JIS) X6175:2006 and Standard ECMA-319 (June 2001).

The total number of servo bands is five, and the total number of databands is four.

A magnetic tape (length of 960 m) on which the servo signal was recordedas described above was wound around the reel of the magnetic tapecartridge (LTO Ultrium 8 data cartridge), and a leader tape according toArticle 9 of Section 3 of standard European Computer ManufacturersAssociation (ECMA)-319 (June 2001) was bonded to an end thereof by usinga commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape waswound around the reel was manufactured.

It can be confirmed by the following method that the magnetic layer ofthe magnetic tape contains a compound formed of polyethyleneimine andstearic acid and having an ammonium salt structure of an alkyl esteranion represented by Formula 1.

A sample is cut out from a magnetic tape, and X-ray photoelectronspectroscopy analysis is performed on the surface of the magnetic layer(measurement area: 300 μm×700 nm) using an ESCA device. Specifically,wide scan measurement is performed by the ESCA device under thefollowing measurement conditions. In the measurement results, peaks areconfirmed at a position of a binding energy of the ester anion and aposition of a binding energy of the ammonium cation.

Device: AXIS-ULTRA manufactured by Shimadzu Corporation

Excited X-ray source: Monochromatic Al-Kα ray

Scan range: 0 to 1,200 eV

Pass energy: 160 eV

Energy resolution: 1 eV/step

Capturing Time: 100 ms/step

Number of times of integration: 5

In addition, a sample piece having a length of 3 cm is cut out from themagnetic tape, and attenuated total reflection-fouriertransform-infrared spectrum (ATR-FT-IR) measurement (reflection method)is performed on the surface of the magnetic layer, and, in themeasurement result, the absorption is confirmed on a wave numbercorresponding to absorption of COO⁻(1,540 cm⁻¹ or 1,430 cm ¹) and a wavenumber corresponding to the absorption of the ammonium cation (2,400cm⁻¹).

Examples 2 to 27 and Comparative Examples 1 to 34

A magnetic tape and a magnetic tape cartridge were obtained by themethod described in Example 1, except that the items shown in Table 1were changed as shown in Table 1.

In Comparative Examples 1 to 11, since the homeotropic alignment processwas not performed, “none” is shown in a column of “homeotropic alignmentprocess conditions” in Table 1.

For Examples 23 to 27 and Comparative Examples 30 to 34, the step afterrecording the servo signal was changed as follows. That is, the heattreatment was performed after recording the servo signal. On the otherhand, in Examples 1 to 22 and Comparative Examples 1 to 29, since suchheat treatment was not performed, “None” was shown in the column of“heat treatment condition” in Table 1.

For Examples 23 to 27 and Comparative Examples 30 to 34, the magnetictape (length of 970 m) after recording the servo signal as described inExample 1 was wound around a core for heat treatment and heat-treated ina state of being wound around the core. As the core for heat treatment,a solid core member (outer diameter: 50 mm) formed of a resin and havinga value of a modulus of bending elasticity shown in Table 1 was used,and the tension in a case of the winding was set as a value shown inTable 1. The heat treatment temperature and heat treatment time in theheat treatment were set to values shown in Table 1. The weight absolutehumidity in the atmosphere in which the heat treatment was performed was10 g/kg Dry air.

After the heat treatment, the magnetic tape and the core for heattreatment were sufficiently cooled, the magnetic tape was detached fromthe core for heat treatment and wound around the core for temporarywinding, and then, the magnetic tape having the final product length(960 m) was wound around the reel of the magnetic tape cartridge (LTOUltrium 8 data cartridge) from the core for temporary winding. Theremaining length of 10 m was cut out and the leader tape based onsection 9 of Standard European Computer Manufacturers Association(ECMA)-319 (June 2001) Section 3 was bonded to the end of the cut sideby using a commercially available splicing tape.

As the core for temporary winding, a solid core member having the sameouter diameter and formed of the same material as the core for heattreatment was used, and the tension at the time of winding was set as0.6 N.

By doing so, a magnetic tape cartridge in which the magnetic tape waswound around the reel was manufactured.

For each of the Examples and Comparative Examples, six magnetic tapecartridges were manufactured, one was used for the evaluation of runningstability below, another one was used for the evaluation of theelectromagnetic conversion characteristics below, and the other fourwere used for the evaluations (1) to (4) of the magnetic tape.

Evaluation of Running Stability

In an environment with a temperature of 32° C. and a relative humidityof 80%, the running stability was evaluated by the following method.

Using each of the magnetic tape cartridges of the examples and thecomparative examples, data recording and reproducing were performedusing the magnetic tape device having the configuration shown in FIG. 8. The arrangement order of the modules included in the recording andreproducing head mounted on the recording and reproducing head unit is“recording module-reproducing module-recording module” (total number ofmodules: 3). The number of magnetic head elements in each module is 32(Ch0 to Ch31), and the element array is configured by sandwiching thesemagnetic head elements between the pair of servo signal readingelements. The reproducing element width of the reproducing elementincluded in the reproducing module is 0.8 nm.

By the following method, the performing of the recording and reproducingof data and evaluating of the running stability during the reproducingwere performed four times in total by sequentially changing the headtilt angle in the order of 0°, 15°, 30°, and 45°. The head tilt angle isan angle θ formed by the axis of the element array of the reproducingmodule with respect to the width direction of the magnetic tape at thestart of each time of running The angle θ was set by the control deviceof the magnetic tape device at the start of each time of running of themagnetic tape, and the head tilt angle was fixed during each time ofrunning of the magnetic tape.

The magnetic tape cartridge was set in the magnetic tape device and themagnetic tape was loaded. Next, while performing servo tracking, therecording and reproducing head unit records pseudo random data having aspecific data pattern on the magnetic tape. The tension applied in thetape longitudinal direction at that time is a constant value. At thesame time with the recording of the data, the value of the servo bandspacing of the entire tape length was measured every 1 m of thelongitudinal position and recorded in the cartridge memory.

Next, while performing servo tracking, the recording and reproducinghead unit reproduces the data recorded on the magnetic tape. The tensionapplied in the tape longitudinal direction at that time is a constantvalue.

The running stability was evaluated using a standard deviation of areading position PES (Position Error Signal) in the width directionbased on the servo signal obtained by the servo signal reading elementduring the reproducing (hereinafter, referred to as “σPES”) as anindicator.

PES is obtained by the following method.

In order to obtain the PES, the dimensions of the servo pattern arerequired. The standard of the dimension of the servo pattern variesdepending on generation of LTO. Therefore, first, an average distance ACbetween the corresponding four stripes of the A burst and the C burstand an azimuth angle α of the servo pattern are measured using amagnetic force microscope or the like.

An average time between 5 stripes corresponding to the A burst and the Bburst over the length of 1 LPOS word is defined as a. An average timebetween 4 stripes corresponding to the A burst and the C burst over thelength of 1 LPOS word is defined as b. At this time, the value definedby AC×(½-a/b)/(2×tan(α)) represents a reading position PES (PositionError Signal) in the width direction based on the servo signal obtainedby the servo signal reading element over the length of 1 LPOS word.Regarding the magnetic tape, an end on a side wound around a reel of themagnetic tape cartridge is referred to as an inner end, an end on theopposite side thereof is referred to as an outer end, the outer end isset to 0 m, and in a region in a tape longitudinal direction over alength of 30 m to 200 m, the standard deviation of PES (σPES) obtainedby the method described above was calculated.

The arithmetic average of PES obtained during four times of recordingand reproducing in total is shown in the column of “σPES” in Table 1. Ina case where the PES is less than 70 nm, it can be determined that therunning stability is excellent.

Evaluation of Electromagnetic Conversion Characteristics(Signal-to-Noise Ratio (SNR))

The magnetic tapes taken out from each of magnetic tape cartridges ofthe examples and the comparative examples were attached to each of the1/2-inch reel testers, and the electromagnetic conversioncharacteristics (signal-to-noise ratio (SNR)) were evaluated by thefollowing methods. In the following evaluation, the head tilt angle wasset to 0°.

In an environment of a temperature of 23° C. and a relative humidity of50%, a tension of 0.70 N was applied in the longitudinal direction ofthe magnetic tape, and recording and reproduction were performed for 10passes. A relative speed of the magnetic head and the magnetic tape wasset as 6 msec. The recording was performed by using a metal-in-gap (MIG)head (gap length of 0.15 nm, track width of 1.0 nm) as the recordinghead and by setting a recording current as an optimal recording currentof each magnetic tape. The reproduction was performed using agiant-magnetoresistive (GMR) head (element thickness of 15 nm, shieldinterval of 0.1 nm, reproducing element width of 0.8 nm) as thereproduction head. A signal having a linear recording density of 350kfci was recorded, the reproduction signal was measured with a spectrumanalyzer manufactured by ShibaSoku Co., Ltd, and an SNR was obtainedfrom the measurement result. In Table 1, the SNR is shown as a relativevalue with respect to Comparative Example 12. In addition, the unit kfciis a unit of linear recording density (cannot be converted to SI unitsystem). As the signal, a sufficiently stabilized portion of the signalafter starting the running of the magnetic tape was used.

Evaluation of Magnetic Tape

(1) Vertical SFD

A sample piece having a size of 3.6 cm×3.2 cm (area: 11.5 cm²) was cutout from each magnetic tape of the examples and the comparativeexamples. For this sample piece, the vertical SFD (measurementtemperature of 25° C.) was obtained by the method described above usinga TM-VSM6050-SM type manufactured by Tamagawa Seisakusho Co., Ltd. as aoscillation sample type magnetic-flux meter.

(2) Frictional Force

The magnetic tape was extracted from each of the magnetic tapecartridges of Examples and Comparative Examples, and the frictionalforce F⁴⁵° and the standard deviation of the frictional force F wereobtained by the method described above in the environment with thetemperature of 32° C. and the relative humidity of 80%. As the LTO8head, a commercially available LTO8 head (manufactured by IBM) was used.

(3) Standard Deviation of Curvature of Magnetic Tape in LongitudinalDirection

The magnetic tape was taken out from the magnetic tape cartridge, andthe standard deviation of the curvature of the magnetic tape in thelongitudinal direction was determined by the method described above.

(4) Tape Thickness

10 tape samples (length: 5 cm) were cut out from any part of themagnetic tape extracted from each of the magnetic tape cartridges ofExamples and Comparative Examples, and these tape samples were stackedto measure the thickness. The thickness was measured using a digitalthickness gauge of a Millimar 1240 compact amplifier manufactured byMARH and a Millimar 1301 induction probe. The value (thickness per tapesample) obtained by calculating 1/10 of the measured thickness wasdefined as the tape thickness. For all of the magnetic tape, the tapethickness was 5.2 nm.

The result described above is shown in Table 1 (Tables 1-1 and 1-2).

TABLE 1-1 Homeotropic Magnetic layer forming composition alignmentprocess Polyethyl- Stearic conditions eneimine acid MagneticFerromagnetic Present Present Projection field Heat treatment conditionspowder or absent or absent formation agent strength Temper- Kind ofadding of adding Kind Amount (T) ature Time Example 1 BaFe Added AddedProjection 1.0 part 0.40 None None formation agent A by mass Example 2BaFe Added Added Projection 1.0 part 0.60 None None formation agent A bymass Example 3 BaFe Added Added Projection 1.0 part 0.75 None Noneformation agent A by mass Example 4 BaFe Added Added Projection 1.0 part0.90 None None formation agent A by mass Example 5 BaFe Added AddedProjection 1.0 part 1.00 None None formation agent A by mass Example 6BaFe Added Added Projection 1.0 part 0.40 None None formation agent B bymass Example 7 BaFe Added Added Projection 1.0 part 0.40 None Noneformation agent C by mass Example 8 BaFe Added Added Projection 1.0 part0.40 None None formation agent D by mass Example 9 BaFe Added AddedProjection 2.0 parts 0.40 None None formation agent A by mass Example 10BaFe Added Added Projection 3.0 parts 0.40 None None formation agent Aby mass Example 11 BaFe Added Added Projection 4.0 parts 0.40 None Noneformation agent A by mass Example 12 BaFe Added Added Projection 2.0parts 0.40 None None formation agent B by mass Example 13 BaFe AddedAdded Projection 3.0 parts 0.75 None None formation agent B by massExample 14 BaFe Added Added Projection 2.0 parts 0.40 None Noneformation agent C by mass Example 15 BaFe Added Added Projection 3.0parts 0.40 None None formation agent C by mass Example 16 BaFe AddedAdded Projection 4.0 parts 0.40 None None formation agent C by massExample 17 BaFe Added Added Projection 2.0 parts 0.40 None Noneformation agent D by mass Example 18 BaFe Added Added Projection 3.0parts 0.90 None None formation agent D by mass Example 19 BaFe AddedAdded Projection 4.0 parts 0.40 None None formation agent D by massExample 20 SrFe1 Added Added Projection 1.0 part 0.75 None Noneformation agent A by mass Example 21 SrFe2 Added Added Projection 1.0part 0.40 None None formation agent A by mass Example 22 ε-iron oxideAdded Added Projection 1.0 part 0.40 None None formation agent A by massExample 23 BaFe Added Added Projection 1.0 part 1.00 50° C. 5 hoursformation agent A by mass Example 24 BaFe Added Added Projection 1.0part 1.00 60° C. 5 hours formation agent A by mass Example 25 BaFe AddedAdded Projection 1.0 part 1.00 70° C. 5 hours formation agent A by massExample 26 BaFe Added Added Projection 1.0 part 1.00 70° C. 15 hours formation agent A by mass Example 27 BaFe Added Added Projection 4.0parts 1.00 70° C. 15 hours  formation agent A by mass Heat treatmentconditions Tension Modulus in case of Standard Standard of bendingwinding deviation deviation of elasticity around F_(45°) of F curvatureσPES Vertical SNR for core the core (gf) (gf) (mm/m) (nm) SFD (dB)Example 1 None None 15 10 6 55 1.5 1.0 Example 2 None None 15 10 6 551.2 1.5 Example 3 None None 15 10 6 55 0.9 2.0 Example 4 None None 15 106 57 0.7 2.5 Example 5 None None 15 10 6 58 0.5 3.0 Example 6 None None14 10 6 53 1.5 1.0 Example 7 None None 13 9 6 51 1.5 1.0 Example 8 NoneNone 13 9 6 54 1.5 1.0 Example 9 None None 10 7 6 50 1.5 1.0 Example 10None None 7 5 6 40 1.5 1.0 Example 11 None None 4 2 6 35 1.5 1.0 Example12 None None 13 8 6 49 1.5 1.0 Example 13 None None 9 5 6 45 0.9 2.0Example 14 None None 10 7 6 47 1.5 1.0 Example 15 None None 8 5 6 43 1.51.0 Example 16 None None 4 2 6 38 1.5 1.0 Example 17 None None 11 7 6 501.5 1.0 Example 18 None None 7 4 6 45 0.7 2.5 Example 19 None None 4 2 633 1.5 1.0 Example 20 None None 15 10 6 55 0.9 2.0 Example 21 None None15 10 6 55 1.5 1.0 Example 22 None None 15 10 6 55 1.5 1.0 Example 230.8 GPa 0.6N 15 10 5 50 0.5 3.0 Example 24 0.8 GPa 0.6N 15 10 4 47 0.53.0 Example 25 0.8 GPa 0.6N 15 10 3 45 0.5 3.0 Example 26 0.8 GPa 0.8N15 10 2 43 0.5 3.0 Example 27 0.8 GPa 0.8N 4 2 2 30 0.5 3.0

TABLE 1-2 Homeotropic Magnetic layer forming composition alignmentprocess Polyethyl- Stearic conditions eneimine acid MagneticFerromagnetic Present Present Projection field Heat treatment conditionspowder or absent or absent formation agent strength Temper- Kind ofadding of adding Kind Amount (T) ature Time Comparative BaFe None AddedProjection 1.0 part None None None Example 1 formation agent E by massComparative BaFe None Added Projection 1.5 parts None None None Example2 formation agent E by mass Comparative BaFe Added Added Projection 1.0part None None None Example 3 formation agent E by mass Comparative BaFeNone Added Projection 1.0 part None None None Example 4 formation agentA by mass Comparative BaFe None Added Projection 2.0 parts None NoneNone Example 5 formation agent A by mass Comparative BaFe None AddedProjection 3.0 parts None None None Example 6 formation agent A by massComparative BaFe None Added Projection 2.0 parts None None None Example7 formation agent B by mass Comparative BaFe None Added Projection 3.0parts None None None Example 8 formation agent B by mass ComparativeBaFe None Added Projection 3.0 parts None None None Example 9 formationagent C by mass Comparative BaFe None Added Projection 0.5 parts NoneNone None Example 10 formation agent E by mass Comparative BaFe AddedAdded Projection 5.0 parts None None None Example 11 formation agent Aby mass Comparative BaFe Added Added Projection 1.0 part 0.30 None NoneExample 12 formation agent A by mass Comparative BaFe Added AddedProjection 1.0 part 0.30 None None Example 13 formation agent B by massComparative BaFe Added Added Projection 1.0 part 0.30 None None Example14 formation agent C by mass Comparative BaFe Added Added Projection 1.0part 0.30 None None Example 15 formation agent D by mass ComparativeBaFe Added Added Projection 2.0 parts 0.30 None None Example 16formation agent A by mass Comparative BaFe Added Added Projection 3.0parts 0.30 None None Example 17 formation agent A by mass ComparativeBaFe Added Added Projection 4.0 parts 0.30 None None Example 18formation agent A by mass Comparative BaFe Added Added Projection 2.0parts 0.30 None None Example 19 formation agent B by mass ComparativeBaFe Added Added Projection 3.0 parts 0.30 None None Example 20formation agent B by mass Comparative BaFe Added Added Projection 2.0parts 0.30 None None Example 21 formation agent C by mass ComparativeBaFe Added Added Projection 3.0 parts 0.30 None None Example 22formation agent C by mass Comparative BaFe Added Added Projection 4.0parts 0.30 None None Example 23 formation agent C by mass ComparativeBaFe Added Added Projection 2.0 parts 0.30 None None Example 24formation agent D by mass Comparative BaFe Added Added Projection 3.0parts 0.30 None None Example 25 formation agent D by mass ComparativeBaFe Added Added Projection 4.0 parts 0.30 None None Example 26formation agent D by mass Comparative SrFe1 Added Added Projection 1.0part 0.30 None None Example 27 formation agent A by mass ComparativeSrFe2 Added Added Projection 1.0 part 0.30 None None Example 28formation agent A by mass Comparative ε-iron oxide Added AddedProjection 1.0 part 0.30 None None Example 29 formation agent A by massComparative BaFe Added Added Projection 1.0 part 0.30 50° C. 5 hoursExample 30 formation agent A by mass Comparative BaFe Added AddedProjection 1.0 part 0.30 60° C. 5 hours Example 31 formation agent A bymass Comparative BaFe Added Added Projection 1.0 part 0.30 70° C. 5hours Example 32 formation agent A by mass Comparative BaFe Added AddedProjection 1.0 part 0.30 70° C. 15 hours  Example 33 formation agent Aby mass Comparative BaFe Added Added Projection 4.0 parts 0.30 70° C. 15hours  Example 34 formation agent A by mass Heat treatment conditionsTension Modulus in case of Standard Standard of bending windingdeviation deviation of elasticity around F_(45°) of F curvature σPESVertical SNR for core the core (gf) (gf) (mm/m] (nm) SFD (dB)Comparative None None 20 15 6 78 2.0 −2.0 Example 1 Comparative NoneNone 19 17 6 73 2.0 −2.0 Example 2 Comparative None None 19 13 6 76 2.0−2.0 Example 3 Comparative None None 20 17 6 77 2.0 −2.0 Example 4Comparative None None 17 16 6 78 2.0 −2.0 Example 5 Comparative NoneNone 19 16 6 75 2.0 −2.0 Example 6 Comparative None None 16 11 6 76 2.0−2.0 Example 7 Comparative None None 16 11 6 75 2.0 −2.0 Example 8Comparative None None 16 11 6 75 2.0 −2.0 Example 9 Comparative NoneNone 19 15 6 85 2.0 −2.0 Example 10 Comparative None None 3 2 6 73 2.0−2.0 Example 11 Comparative None None 15 10 6 55 1.7 0 Example 12Comparative None None 14 10 6 53 1.7 0 Example 13 Comparative None None13 9 6 51 1.7 0 Example 14 Comparative None None 13 9 6 54 1.7 0 Example15 Comparative None None 10 7 6 50 1.7 0 Example 16 Comparative NoneNone 7 5 6 40 1.7 0 Example 17 Comparative None None 4 2 6 35 1.7 0Example 18 Comparative None None 13 8 6 49 1.7 0 Example 19 ComparativeNone None 9 5 6 45 1.7 0 Example 20 Comparative None None 10 7 6 47 1.70 Example 21 Comparative None None 8 5 6 43 1.7 0 Example 22 ComparativeNone None 4 2 6 38 1.7 0 Example 23 Comparative None None 11 7 6 50 1.70 Example 24 Comparative None None 7 4 6 45 1.7 0 Example 25 ComparativeNone None 4 2 6 33 1.7 0 Example 26 Comparative None None 15 10 6 55 1.70 Example 27 Comparative None None 15 10 6 55 1.7 0 Example 28Comparative None None 15 10 6 55 1.7 0 Example 29 Comparative 0.8 GPa0.6N 15 10 5 50 1.7 0 Example 30 Comparative 0.8 GPa 0.6N 15 10 4 47 1.70 Example 31 Comparative 0.8 GPa 0.6N 15 10 3 45 1.7 0 Example 32Comparative 0.8 GPa 0.8N 15 10 2 43 1.7 0 Example 33 Comparative 0.8 GPa0.8N 4 2 2 30 1.7 0 Example 34

From the results shown in Table 1, the magnetic tapes of the examples inwhich both the frictional force F₄₅° and the standard deviation of thefrictional force F measured in the environment with the temperature of32° C. and the relative humidity of 80% were in the ranges describedabove showed excellent running stability in a case of allowing themagnetic tape run at different head tilt angles in the high temperatureand high humidity environment.

In addition, from the results shown in Table 1, it can be confirmed thatthe magnetic tape of the examples in which the vertical SFD is 1.5 orless exhibited excellent electromagnetic conversion characteristics.

One aspect of the invention is advantageous in a technical field ofvarious data storages.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer containing a ferromagnetic powder, whereina vertical switching field distribution SFD of the magnetic tape is 1.5or less, and in an environment with a temperature of 32° C. and arelative humidity of 80%, a frictional force F₄₅° on a surface of themagnetic layer with respect to an LTO8 head measured at a head tiltangle of 45° is 4 gf to 15 gf, and a standard deviation of a frictionalforce F on the surface of the magnetic layer with respect to the LTO8head measured at each of head tilt angles of 0°, 15°, 30°, and 45° is 10gf or less.
 2. The magnetic tape according to claim 1, wherein thestandard deviation of F is 2 gf to 10 gf.
 3. The magnetic tape accordingto claim 1, wherein the vertical switching field distribution SFD of themagnetic tape is 0.5 to 1.5.
 4. The magnetic tape according to claim 1,wherein a standard deviation of curvature of the magnetic tape in alongitudinal direction is 5 mm/m or less.
 5. The magnetic tape accordingto claim 1, wherein the magnetic layer contains inorganic oxide-basedparticles.
 6. The magnetic tape according to claim 5, wherein theinorganic oxide-based particles are composite particles of an inorganicoxide and a polymer.
 7. The magnetic tape according to claim 1, whereinthe magnetic layer contains carbon black.
 8. The magnetic tape accordingto claim 1, further comprising: a non-magnetic layer containing anon-magnetic powder between the non-magnetic support and the magneticlayer.
 9. The magnetic tape according to claim 1, further comprising: aback coating layer containing a non-magnetic powder on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer.
 10. The magnetic tape according to claim 1, wherein atape thickness is 5.2 μm or less.
 11. The magnetic tape according toclaim 1, wherein the standard deviation of F is 2 gf to 10 gf, thevertical switching field distribution SFD of the magnetic tape is 0.5 to1.5, a standard deviation of curvature of the magnetic tape in alongitudinal direction is 5 mm/m or less, the magnetic layer containscomposite particles of an inorganic oxide and a polymer, the magnetictape further comprises: a non-magnetic layer containing a non-magneticpowder between the non-magnetic support and the magnetic layer, and aback coating layer containing a non-magnetic powder on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer, and a tape thickness is 5.2 μm or less.
 12. The magnetictape according to claim 1, wherein the standard deviation of F is 2 gfto 10 gf, the vertical switching field distribution SFD of the magnetictape is 0.5 to 1.5, a standard deviation of curvature of the magnetictape in a longitudinal direction is 5 mm/m or less, the magnetic layercontains carbon black, the magnetic tape further comprises: anon-magnetic layer containing a non-magnetic powder between thenon-magnetic support and the magnetic layer, and a back coating layercontaining a non-magnetic powder on a surface side of the non-magneticsupport opposite to a surface side provided with the magnetic layer, anda tape thickness is 5.2μm or less.
 13. A magnetic tape cartridgecomprising: the magnetic tape according to claim
 1. 14. A magnetic tapedevice comprising: the magnetic tape according to claim
 1. 15. Themagnetic tape device according to claim 14, further comprising: amagnetic head, wherein the magnetic head includes a module having anelement array including a plurality of magnetic head elements between apair of servo signal reading elements, and the magnetic tape devicechanges an angle θ formed by an axis of the element array with respectto a width direction of the magnetic tape during running of the magnetictape in the magnetic tape device.